Abstract: According to the technological requirements of the reverse machining of the main reducer housing on the vertical special CNC lathe and the structural characteristics of the workpiece, a special turning fixture which can adapt to many varieties and easy to install is designed and manufactured. It solves the efficient machining of a machine tool which can quickly switch the outer circle of the gland of the main reducer housing of various models by changing the positioning plate. The hydraulic clamping cylinder is set in the spindle of the machine tool to realize the automatic hydraulic clamping of the workpiece and reduce the labor intensity of the workers.The production practice proves that the fixture is simple and reliable, easy to operate, improves production efficiency and ensures machining accuracy.