CAD/CAM systems provide the possibility to integrate with NC post-processors, so the NC program can directly execute post-processing in a CAM system. But surveys taken by CAM users indicated that producing a formatted NC program remained to be one of their most perplexing problems. In this paper, based on the general introduction of the NC post-processing, the authors discussed the important roles of post-processing in NC modules, and analyzed some problems in popular post-processors integrated with CAM system. This paper also recommended some famous post-processing products and their features. At last some suggestions and a sample post-processing of parallel machine were given to solve the problems.