The utility model discloses an inner clamping fixing device for surface machining of a three-way ball valve. The inner clamping fixing device for surface machining of the three-way ball valve comprises a base, a first support, a second support, a first inner clamping part, a second inner clamping part, a cutter frame, a cutter holder, a cutter and a numerical control unit, wherein the first support and the second support are arranged at the two ends of the base respectively, the first inner clamping part is installed on the first support through a first driving mechanism, the second inner clamping part is installed on the second support through a second driving mechanism, the first inner clamping part and the second inner clamping part are arranged in an opposite mode, the cutter frame is installed on a sliding rail arranged on the top surface of the base through a third driving mechanism, the cutter holder is installed on the cutter frame through a fourth driving mechanism, the cutter is installed on the cutter holder through a fifth driving mechanism, and the numerical control unit is electrically connected with the first driving mechanism, the second driving mechanism, the third driving mechanism, the fourth driving mechanism and the fifth driving mechanism, and has control over clamping fixation and surface machining of the three-way ball valve. According to the inner clamping fixing device for surface machining of the three-way ball valve, machining can be conveniently and accurately carried out on the surface of the three-way ball valve.