What is claimed is:1. An energy saving method, applied to a communications system, wherein the communications system comprises a centralized controller and m radio remote units (RRUs) connected to the centralized controller, wherein m is an integer greater than 1, and wherein the energy saving method comprises:determining, by the centralized controller, n RRUs in the m RRUs, wherein a sum of first downlink reference signal received powers (RSRPs) of a same terminal, corresponding to the n RRUs, is greater than or equal to a first preset value, wherein one RRU corresponds to first downlink RSRPs of a plurality of terminals, wherein a first downlink RSRP of one terminal corresponding to one RRU is a received power that is estimated by the centralized controller, that is measured by the terminal, and that is of a reference signal (RS) from the RRU at a corresponding first RS transmit power, wherein a first RS transmit power corresponding to one RRU is an RS transmit power obtained after power boosting is performed on a second RS transmit power corresponding to the RRU, wherein second RS transmit powers corresponding to the m RRUs are all preconfigured, wherein the first preset value is a level value to be reached when the plurality of terminals perform a downlink service, and wherein n is an integer greater than 0 and less than m; andin response to determining the n RRUs in the m RRUs:turning off, by the centralized controller, an RRU that is in the m RRUs and that is different from the n RRUs; andboosting, by the centralized controller, a second RS transmit power corresponding to each of the n RRUs to a corresponding first RS transmit power, and enabling each of the n RRUs to send an RS at the corresponding first RS transmit power.2. The energy saving method according to claim 1, wherein the boosting, by the centralized controller, a second RS transmit power corresponding to each of the n RRUs to a corresponding first RS transmit power comprises:reducing, by the centralized controller, data transmit power, and increasing RS transmit power to boost the second RS transmit power corresponding to each of the n RRUs to the corresponding first RS transmit power; orconcentrating, by the centralized controller, a total RS transmit power on a service bandwidth of a logical cell to which the RRU belongs to a bandwidth in a middle of the service bandwidth to boost the second RS transmit power corresponding to each of the n RRUs to the corresponding first RS transmit power.3. The energy saving method according to claim 1, wherein before the determining, by the centralized controller, n RRUs in the m RRUs, the energy saving method further comprises:determining, by the centralized controller, second downlink RSRPs of the plurality of terminals corresponding to each of the m RRUs, wherein a second downlink RSRP of one terminal corresponding to one RRU is a received power that is measured by the terminal and that is of an RS from the RRU at a corresponding second RS transmit power;determining, by the centralized controller, a boosted RS transmit power of each of the m RRUs; anddetermining, by the centralized controller, first downlink RSRPs of the plurality of terminals corresponding to each of the m RRUs based on the second downlink RSRPs of the plurality of terminals corresponding to each of the m RRUs and the boosted RS transmit power of each RRU.4. The energy saving method according to claim 2, wherein before the concentrating, by the centralized controller, a total RS transmit power on a service bandwidth of a logical cell to which the RRU belongs to a bandwidth in a middle of the service bandwidth to boost the second RS transmit power corresponding to each of the n RRUs to the corresponding first RS transmit power, the energy saving method further comprises:determining, by the centralized controller based on a boosted RS transmit power of each of the n RRUs, the bandwidth in the middle corresponding to the n RRUs.5. The energy saving method according to claim 3, wherein that the centralized controller determines a second downlink RSRP of a first terminal corresponding to a first RRU in the m RRUs comprises:measuring, by the centralized controller, uplink RSRPs of the first terminal corresponding to the m RRUs, wherein an uplink RSRP of the first terminal corresponding to one RRU is a received power that is measured by the centralized controller and that is of a sounding reference signal (SRS) from the first terminal through the RRU, and wherein the first terminal is any one of the plurality of terminals;receiving, by the centralized controller, information that is from the first terminal and that is about a sum of second downlink RSRPs of the first terminal corresponding to the m RRUs; anddetermining, by the centralized controller, the second downlink RSRP of the first terminal corresponding to the first RRU based on the uplink RSRPs of the first terminal corresponding to the m RRUs and the information about the sum of the second downlink RSRPs of the first terminal corresponding to the m RRUs, wherein the first RRU is any one of the m RRUs.6. The energy saving method according to claim 5, wherein the determining, by the centralized controller, the second downlink RSRP of the first terminal corresponding to the first RRU based on the uplink RSRPs of the first terminal corresponding to the m RRUs and the information about the sum of the second downlink RSRPs of the first terminal corresponding to the m RRUs comprises:determining, by the centralized controller based on a preset algorithm, a linear value of the second downlink RSRP of the first terminal corresponding to the first RRU, wherein the preset algorithm iswherein Suplink RSRP is a sum of linear values of the uplink RSRPs of the first terminal corresponding to the m RRUs, wherein Sdownlink RSRP is a sum of linear values of the second downlink RSRPs of the first terminal corresponding to the m RRUs, wherein RSRP1′ is a linear value of an uplink RSRP of the first terminal corresponding to the first RRU, and wherein RSRP1 is the linear value of the second downlink RSRP of the first terminal corresponding to the first RRU; anddetermining, by the centralized controller, the second downlink RSRP of the first terminal corresponding to the first RRU based on the linear value of the second downlink RSRP of the first terminal corresponding to the first RRU.7. The energy saving method according to claim 1, wherein the determining, by the centralized controller, n RRUs in the m RRUs comprises:determining, by the centralized controller, whether a sum of first downlink RSRPs of each of the plurality of terminals corresponding to any j RRUs in the m RRUs is greater than or equal to the first preset value; andif the sum of the first downlink RSRPs of each of the plurality of terminals corresponding to the j RRUs in the m RRUs is greater than or equal to the first preset value, determining, by the centralized controller, the j RRUs as the n RRUs; orif the sum of the first downlink RSRPs of each of the plurality of terminals corresponding to the j RRUs in the m RRUs is less than the first preset value, assigning, by the centralized controller, j=j+1, and continuing to determine whether a sum of first downlink RSRPs of each of the plurality of terminals corresponding to any j RRUs in the m RRUs is greater than or equal to the first preset value, until the n RRUs are determined, wherein an initial value of j is a preset value.8. The energy saving method according to claim 1, wherein before the determining, by the centralized controller, n RRUs in the m RRUs, the energy saving method further comprises:determining, by the centralized controller, that the communications system is to enter an energy saving mode.9. An energy saving apparatus, comprising:at least one processor; anda memory coupled to the at least one processor and storing executable instructions for execution by the at least one processor to:determine n radio remote units (RRUs) in m RRUs, wherein a sum of first downlink reference signal received powers (RSRPs) of a same terminal, corresponding to the n RRUs, is greater than or equal to a first preset value, wherein one RRU corresponds to first downlink RSRPs of a plurality of terminals, wherein a first downlink RSRP of one terminal corresponding to one RRU is a received power that is estimated by the processor, that is measured by the terminal, and that is of a reference signal (RS) from the RRU at a corresponding first RS transmit power, wherein a first RS transmit power corresponding to one RRU is an RS transmit power obtained after power boosting is performed on a second RS transmit power corresponding to the RRU, wherein second RS transmit powers corresponding to the m RRUs are all preconfigured, wherein the first preset value is a level value to be reached when the plurality of terminals perform a downlink service, and wherein n is an integer greater than 0 and less than m; andin response to determining the n RRUs in the m RRUs:turn off an RRU that is in the m RRUs and that is different from the n RRUs; andboost a second RS transmit power corresponding to each of the n RRUs to a corresponding first RS transmit power, and enabling each of the n RRUs to send an RS at the corresponding first RS transmit power.10. The energy saving apparatus according to claim 9, wherein the executable instructions are for execution by the at least one processor to:reduce data transmit power, and increase RS transmit power to boost the second RS transmit power corresponding to each of the n RRUs to the corresponding first RS transmit power; orconcentrate a total RS transmit power on a service bandwidth of a logical cell to which the RRU belongs to a bandwidth in a middle of the service bandwidth to boost the second RS transmit power corresponding to each of the n RRUs to the corresponding first RS transmit power.11. The energy saving apparatus according to claim 9, wherein the executable instructions are for execution by the at least one processor to:determine second downlink RSRPs of the plurality of terminals corresponding to each of the m RRUs, wherein a second downlink RSRP of one terminal corresponding to one RRU is a received power that is measured by the terminal and that is of an RS from the RRU at a corresponding second RS transmit power;determine a boosted RS transmit power of each of the m RRUs; anddetermine first downlink RSRPs, of the plurality of terminals corresponding to each of the m RRUs based on the second downlink RSRPs of the plurality of terminals corresponding to each of the m RRUs and the boosted RS transmit power of each RRU.12. The energy saving apparatus according to claim 10, wherein the executable instructions are for execution by the at least one processor to:determine, based on a boosted RS transmit power of each of the n RRUs, the bandwidth in the middle corresponding to the n RRUs.13. The energy saving apparatus according to claim 11, wherein the executable instructions are for execution by the at least one processor to:measure uplink RSRPs of a first terminal corresponding to the m RRUs, wherein an uplink RSRP of the first terminal corresponding to one RRU is a received power that is measured by the processor and that is of a sounding reference signal (SRS) from the first terminal through the RRU, and wherein the first terminal is any one of the plurality of terminals;receive information that is from the first terminal and that is about a sum of second downlink RSRPs of the first terminal corresponding to the m RRUs; anddetermine a second downlink RSRP of the first terminal corresponding to a first RRU based on the uplink RSRPs of the first terminal corresponding to the m RRUs and the information about the sum of the second downlink RSRPs of the first terminal corresponding to the m RRUs, wherein the first RRU is any one of the m RRUs.14. The energy saving apparatus according to claim 13, wherein the executable instructions are for execution by the at least one processor to:determine based on a preset algorithm, a linear value of the second downlink RSRP of the first terminal corresponding to the first RRU, wherein the preset algorithm iswherein Suplink RSRP is a sum of linear values of the uplink RSRPs of the first terminal corresponding to the m RRUs, wherein Sdownlink RSRPis a sum of linear values of the second downlink RSRPs of the first terminal corresponding to the m RRUs, wherein RSRP1′ is a linear value of an uplink RSRP of the first terminal corresponding to the first RRU, and wherein RSRP1 is the linear value of the second downlink RSRP of the first terminal corresponding to the first RRU; anddetermine the second downlink RSRP of the first terminal corresponding to the first RRU based on the linear value of the second downlink RSRP of the first terminal corresponding to the first RRU.15. The energy saving apparatus according to claim 9, wherein the executable instructions are for execution by the at least one processor to:determine whether a sum of first downlink RSRPs of each of the plurality of terminals corresponding to any j RRUs in the m RRUs is greater than or equal to the first preset value; andif the sum of the first downlink RSRPs of each of the plurality of terminals corresponding to the j RRUs in the m RRUs is greater than or equal to the first preset value, determine the j RRUs as the n RRUs; orif the sum of the first downlink RSRPs of each of the plurality of terminals corresponding to the j RRUs in the m RRUs is less than the first preset value, assign j=j+1, and continue to determine whether a sum of first downlink RSRPs of each of the plurality of terminals corresponding to any j RRUs in the m RRUs is greater than or equal to the first preset value, until the n RRUs are determined, wherein an initial value of j is a preset value.16. The energy saving apparatus according to claim 9, wherein the executable instructions are for execution by the at least one processor to:determine that the energy saving apparatus is to enter an energy saving mode.17. A non-transitory computer-readable storage medium, comprising an instruction for execution by a computer to:determine n radio remote units (RRUs) in m RRUs, wherein a sum of first downlink reference signal received powers (RSRPs) of a same terminal, corresponding to the n RRUs, is greater than or equal to a first preset value, wherein one RRU corresponds to first downlink RSRPs of a plurality of terminals, wherein a first downlink RSRP, of one terminal, corresponding to one RRU is a received power that is estimated by the computer, that is measured by the terminal, and that is of a reference signal (RS) from the RRU at a corresponding first RS transmit power, wherein a first RS transmit power corresponding to one RRU is an RS transmit power obtained after power boosting is performed on a second RS transmit power corresponding to the RRU, wherein second RS transmit powers corresponding to the m RRUs are all preconfigured, wherein the first preset value is a level value to be reached when the plurality of terminals perform a downlink service, and wherein n is an integer greater than 0 and less than m; andin response to determining the n RRUs in the m RRUs:turn off an RRU that is in the m RRUs and that is different from the n RRUs; andboost a second RS transmit power corresponding to each of the n RRUs to a corresponding first RS transmit power, and enabling each of the n RRUs to send an RS at the corresponding first RS transmit power.18. The non-transitory computer-readable storage medium according to claim 17, wherein the instruction is for execution by the computer to:reduce data transmit power, and increase RS transmit power to boost the second RS transmit power corresponding to each of the n RRUs to the corresponding first RS transmit power; orconcentrate a total RS transmit power on a service bandwidth of a logical cell to which the RRU belongs to a bandwidth in a middle of the service bandwidth to boost the second RS transmit power corresponding to each of the n RRUs to the corresponding first RS transmit power.19. The non-transitory computer-readable storage medium according to claim 18, wherein the instruction is for execution by the computer to:determine, based on a boosted RS transmit power of each of the n RRUs, the bandwidth in the middle corresponding to the n RRUs.20. The non-transitory computer-readable storage medium according to claim 17, wherein the instruction is for execution by the computer to:determine that the computer is to enter an energy saving mode.