In order to solve the problems existing in geometric simulation of cutting process, slice segmentation method was presented in this paper. The instantaneous shape of roughcasts which are cut can be represented by the characteristics set that can be obtained through proper slice of machined parts and the intersection calculation of cutter and machined parts. By using this method, the accurate result of intersection calculation can be accurate and be gotten rapidly. Besides, because this method is based on visual C++ and OpenGL, it can be isolated from the commercial software. The method is proved to be feasible by the cutting simulation example of cylinder gears and bevel gears.