Post-processing technology is the key to CNC automatic programming technology and an important module of the CAD / CAM system. Post-processing technology converts the NC program that is produced by the CNC automatic programming tool into the file that can be identified by CNC system. Moreover, the generated tool path files must match with the CNC system. Post-processing techniques and UG software are briefly introduced. Using them, a post-processor for FANUC CNC systems is created. The program that generated by the special processor is contrasted with the general processor. The results illustrat that using the dedicated post-processor in engineering applications can improve programming efficiency and processing reliability.