In order to avoid interference in NC milling process, a milling simulation design method of NC system based on 3D modeling technology is proposed. We use OpenGL technology and advanced object-oriented programming technology to perform a comprehensive object-oriented design of the NC milling simulation software system. On this basis, the tool motion parameters in the NC code are extracted and stored, the STL model is introduced as the data model of the machining object, and the interface mechanism between OpenGL and VC is provided. Finally, through the main interface of Visual C++ application program, the development of database and application system oriented to 3D end mill model is realized. The simulation results show that the method presented in this paper is more realistic for the establishment of the whole virtual milling machine profile, and it is suitable for general or more complex parts NC machining programming and simulation.