Abstract: An improved algorithm for Z-map and Z-buffer was proposed according to the common simulation frame of machining process to optimize the simulation system so as to verify NC programs and improving machining conditions. Introducing the idea about the useful sideline into the simulation process, the repeated operation of different comparisons are compacted, with the Z-buffer restructured from Z-map by way of height interpolation and the computational complexity of cutting process reduced through reference planes. Moreover, a multi-thread approach is proposed as an implementation frame to improve the practicality of the algorithm. Testing data show that the algorithm is of high efficiency in practice and the multi-thread frame can serve the function of making the simulation more reasonable and the response speed quicker.