The invention specifically relates to a three-hole socket. The three-hole socket comprises a bottom casing and a surface casing fixed on the bottom casing, wherein the surface casing is provided with a lock pin, the bottom casing is internally provided with a protective door moving up and down along the inside of the bottom casing, the protective door is divided into a first protective door, a second protective door and a third protective door , the side positions of the first protective door and the second protective door are each provided with a slide wall, one end of the lock pin is arranged on the slide walls, the third protective door is provided with a lock key, and the lock key is arranged on the lock pin. The three-hole socket has the following advantages: 1, by use of combination of the lock pin and the protective door, the protective door cannot be open simply through push at one side without simultaneous arrangement of a standard plug on the protective door, and thus a safety protection effect is exhibited; and 2,the lock pin is locked by use of a first lock pin and a second lock pin for restricting unlocking which cannot be realized without a plug, children are prevented from electric shock risks caused by insertion of metal probes into the socket, and an electric shock prevention effect is exhibited.