Efficient and exact collision detection is important to improve reality and enhance immersion of virtual environment of NC(numerical control) lathe system. We introduce two techniques to improve efficiency and speed up the collision detection process. First, we adopt a spatial partitioning system and bounding volumes hierarchies to reduce the number of potential colliding polygons. Octree structure has been adopted to describe the partitioned object. Second, according to the feature of NC lathe system ,we exploit cylinders to simulate the workpieces. The experiments testify that the algorithm accelerates the velocity of collision detection and ensures the real_time requirement of collision detection in virtual dynamic processing environment.