The method of machining negative pressure angle spiral clutches with disc milling cutter and gear milling machine is studied. The mathematical model is established according to the characteristics of spiral clutches firstly, and the coordinate transformation relationship from the cutting tool system to workpiece system, the tooth surface points and mismatch quantity are calculated after selecting the appropriate initial value of the surface coordinates. Based on the above analysis, the 3D model of the clutch and mismatch analysis are completed after an example is introduced. To verify the tooth surface calculation theory, the machining simulation is carried out. The correctness of calculation and the feasibility of method are verified.