Numerical control milling machine with a special transformation can be achieved the involute path processing functions. By using Fan method to process a way to synthesize involute track requirements and involute contour processing. This method is particularly suitable for gear modulus m ≥ 12 ~ 40 of the big modulus gear machining, and omit the big modulus gear-specific complex tool manufacturing. Another advantage is that as the basic parameters of the coordinates programming trajectory calculation as a way to carry out involute trajectories run control, gears accuracy can be effective control and assurance. Furthermore, it can be revised and the edge of the involute tooth surface in the tangential connection.