In view of the limitation of trial cutting or manual inspection of the process planning validation of conventional numerical control, a new method of planning process simulation based on virtual reality was proposed. Firstly, the structure and implementation scheme of simulation system were given, and the simulation platform was established. Then, the movement behavior of machine tool was analyzed in details, an event handle model based on message response mechanism was proposed. Take tool change for example, the behavior module and the motion mode of related components were described. Researched and inferred the solving process of the curved surface of tool sweeping. The NC code compiler and cutting process simulation were expounded. Finally, the system was realized by means of using Visual C++6.0, OpenGL, Virtools and so on, It could verify the rationality of process planning and achieve the accurate assess.