Abstract: NC machining is widely used for workpieces with complex processes, this requires highly technical ability and experience of programmers, in order to reduce labor costs, we can use the secondary development function of open CNC system to package complex processes and huge NC codes into special functions of CNC system, using this function for processing programming and operation, there are guided prompts and graphical instructions, which greatly reduce the requirements of technical experience and skills for programming and operating operators. Meanwhile, programming efficiency and operation accuracy also can be improved. Maximize the advantages and the values of open CNC systems.