Abstract: Under the guidance of new trend of CAD/CAM system development and standardization,NC programming system is introducing the concepts of parameterization and intelligence, where machining trajectories generation is dynamically associated with the product design process,and thus,can respond in real time to the latter's modification.The unified representation of the machining region in process planning is build up on the history-based design model recogni-tion and its automatic conversion to manufacturing model.By capturing the original explicit design semantics and design process,the general NC computation model could be set up and expressed as 'a pocket and its boundary'.This model is beyond the reach of traditional feature model and supports initiative process planning,which favors the generation of high quality NC program to meet the design requirements in a greater degree.