That the UE meets the preset third condition includes: before the second processing unit 604 executes the data sending or receiving process in the PS domain of the 2G/3G network, when the UE receives the Paging message through the LTE network but does not receive the paging message through the PS domain of the 2G/3G network, and the signal strength of the LTE network does not meet the data sending or receiving requirement, the second Paging message processing unit 607 does not respond to the paging message that is received through the LTE network; if the UE receives the Paging message through the PS domain of the 2G/3G network after receiving the Paging message through the LTE network, the second Paging message processing unit 607 sends the service request message to the SGSN in the 2G/3G network; or, when the UE receives the Paging message through the PS domain of the 2G/3G network but does not receive the paging message through the LTE network, and the signal strength of the LTE network meets the data sending or receiving requirement, if the UE does not receive the Paging message through the LTE network within the preset third period of time after receiving the Paging message through the PS domain of the 2G/3G network, the second Paging message processing unit 607 sends the service request message to the SGSN in the 2G/3G network; or, when the UE receives the Paging message through the PS domain of the 2G/3G network but does not receive the paging message through the LTE network, and the signal strength of the LTE network does not meet the data sending or receiving requirement, the second Paging message processing unit 607 sends the service request message to the SGSN in the 2G/3G network.