What is claimed is:1. A dummy chassis, comprising:a first frame bar having a first long side and a first engaging portion;a second frame bar having a second long side and a second engaging portion; anda connection member having a first end portion and a second end portion which are located oppositely, the first end portion having a third engaging portion, the second end portion having a fourth engaging portion, the connection member that is formed with a sunken portion, the sunken portion that is formed with a bottom portion and an inner wall being adjacent to the bottom portion, and a width of the connection member is less than a length of the first frame bar and a length of the second frame bar,wherein, when the first frame bar, the second frame bar and the connection member are combined into a first appearance, the first end portion of the connection member is connected to the first long side of the first frame bar, and the third engaging portion of the connection member is detachably connected to the first engaging portion of the first frame bar, and the second end portion of the connection member is connected to the second long side of the second frame bar, and the fourth engaging portion of the connection member is detachably connected to the second engaging portion of the second frame bar, when the first frame bar, the second frame bar and the connection member are combined into a second appearance, the first frame bar and the second frame bar are detachably located at the bottom portion of the sunken portion, respectively, and the second frame bar is located between the first frame bar and the inner wall of the sunken portion.2. The dummy chassis of claim 1, wherein the first engaging portion comprises a first elastic arm and a first fixing block which is disposed on the first elastic arm, and the third engaging portion comprises a first fixing opening,wherein the first end portion of the connection member is detachably connected to the first long side of the first frame bar through the first fixing block being engaged with the first fixing opening.3. The dummy chassis of claim 1, wherein the second engaging portion comprises a second elastic arm and a second fixing block which is disposed on the second elastic arm, and the fourth engaging portion comprises a second fixing opening,wherein the second end portion of the connection member is detachably connected to the second long side of the second frame bar through the second fixing block being engaged with the second fixing opening.4. The dummy chassis of claim 1, wherein the first frame bar is formed with a first inlet, a first sliding groove and a second sliding groove, the first inlet is formed on the first long side of the first frame bar, and located between the first sliding groove and the second sliding groove, wherein the first sliding groove and the second sliding groove are vertically staggered from each other; andthe second frame bar is formed with a second inlet, a first fixing slot and a second fixing slot, the second inlet is formed on the second long side of the second frame bar, and located between the first fixing slot and the second fixing slot,wherein the first fixing slot and the second fixing slot are vertically staggered from each other, and the first sliding groove and the first fixing slot are commonly disposed at a first height, and the second sliding groove and the second fixing slot are commonly disposed at a second height which is different from the first height.5. The dummy chassis of claim 4, wherein the connection member is provided with two first protruding portions and two second protruding portions, each of the two first protruding portions and each of the two second protruding portions are oppositely arranged to two long side surfaces of the connection member which are opposite to each other,wherein, when the first end portion of the connection member is located at the first inlet, and the second end portion thereof is located at the second inlet, the first protruding portions respectively insert into the first sliding groove and the first fixing slot which are located at the same height, and the second protruding portions respectively insert into the second sliding groove and the second fixing slot which are located at the same height.6. The dummy chassis of claim 1, wherein one side of the second frame bar being opposite to the second long side is provided with two positioning pins which are spaced arranged.7. The dummy chassis of claim 1, wherein the first frame bar comprises two elastic buckles, which are respectively located at two opposite ends of the first frame bar.8. The dummy chassis of claim 1, wherein the first appearance is in an “H” shape.9. The dummy chassis of claim 1, wherein the connection member comprises a plurality of position-limiting ribs, the position-limiting ribs are separately arranged on the inner wall of the sunken portion, the second frame bar is formed with a plurality of position-limiting slots, the position-limiting slots are separately arranged on one surface of the second frame bar,wherein the second frame bar is sandwiched between the position-limiting ribs and the bottom portion of the sunken portion through the position-limiting ribs respectively extending into the position-limiting slots.10. The dummy chassis of claim 9, wherein the connection member further comprises two position-limiting lugs, the position-limiting lugs are separately arranged on the bottom portion of the sunken portion, and each of the two position-limiting lugs is formed with a position-limiting opening; andthe first frame bar comprises two elastic buckles, which are respectively located at two opposite ends of the first frame bar,wherein the first frame bar is fixed between the two position-limiting lugs through the two elastic buckles respectively extending into the position-limiting openings.11. A server rack, comprising:a rack body having a front end and a rear end which are opposite to each other;two sliding rails fixedly connected to two opposite inner sides of the rack body, respectively;a power socket disposed on the rear end of the rack body; anda dummy chassis that is slidably disposed on the two sliding rails, and comprising:a first frame bar disposed on the front end of the rack body, and provided with a first long side;a second frame bar covering the power socket, and provided with a second long side; anda connection member having a first end portion and a second end portion which are located oppositely, the first end portion being detachably connected to the first long side of the first frame bar, and the second end portion being detachably connected to the second long side of the second frame bar, wherein the connection member is further formed with a sunken portion, the sunken portion is formed with a bottom portion and an inner wall being adjacent to the bottom portion,wherein a width of the connection member is less than a length of the first frame bar and a length of the second frame bar,when the dummy chassis is idle, the first frame bar and the second frame bar are allowed to be detachably located at the bottom portion of the sunken portion, respectively, and the second frame bar is located between the first frame bar and the inner wall of the sunken portion.12. The server rack of claim 11, wherein the first frame bar comprises a first elastic arm and a first fixing block which is disposed on the first elastic arm, and the first end portion of the connection member comprises a first fixing opening,wherein the first end portion of the connection member is detachably connected to the first long side of the first frame bar through the first fixing block being engaged with the first fixing opening.13. The server rack of claim 11, wherein the second frame bar comprises a second elastic arm and a second fixing block which is disposed on the second elastic arm, and the second end portion of the connection member comprises a second fixing opening,wherein the second end portion of the connection member is detachably connected to the second long side of the second frame bar through the second fixing block being engaged with the second fixing opening.14. The server rack of claim 11, wherein the first frame bar is formed with a first inlet, a first sliding groove and a second sliding groove, the first inlet is formed on the first long side of the first frame bar, and located between the first sliding groove and the second sliding groove, wherein the first sliding groove and the second sliding groove are vertically staggered from each other; andthe second frame bar is formed with a second inlet, a first fixing slot and a second fixing slot, the second inlet is formed on the second long side of the second frame bar, and located between the first fixing slot and the second fixing slot,wherein the first fixing slot and the second fixing slot are vertically staggered from each other, and the first sliding groove and the first fixing slot are commonly disposed at a first height, and the second sliding groove and the second fixing slot are commonly disposed at a second height which is different from the first height.15. The server rack of claim 14, wherein the connection member is provided with two first protruding portions and two second protruding portions, each of the two first protruding portions and each of the two second protruding portions are oppositely arranged to two long side surfaces of the connection member which are opposite to each other,wherein, when the first end portion of the connection member is located at the first inlet, and the second end portion thereof is located at the second inlet, the first protruding portions respectively insert into the first sliding groove and the first fixing slot which are located at the same height, and the second protruding portions respectively insert into the second sliding groove and the second fixing slot which are located at the same height.16. The server rack of claim 11, wherein the second frame bar comprises two positioning pins which are spaced arranged on one side of the second frame bar being opposite to the second long side; andeach of the two sliding rails is provided with a positioning hole, the positioning holes are respectively disposed on the rear end of the rack body, and the two positioning pins are removably disposed into the positioning holes, respectively.17. The server rack of claim 11, wherein the first frame bar comprises two elastic buckles, which are respectively located at two opposite ends of the first frame bar; andeach of the two sliding rails is formed with a limiting hole, and the limiting holes are disposed on the front end of the rack body, and the elastic buckles are removably disposed in the limiting holes, respectively.18. The server rack of claim 11, wherein the dummy chassis is in an “H” shape.