与传统的集中式刀具轨迹计算方法不同，基于ＮＣ特征单元，把刀具轨迹计算分为两步完成，以此改善数控加工系统的可集成性、可视性和可控性．给出了抽象ＮＣ特征单元及适合２．５轴区域加工的环切特征单元的定义，提出了通过链接划分法生成环切特征单元，以及通过环切特征单元计算刀具轨迹的算法． Different from the traditional method of calculating the tool path, the calculation of tool path is divided into two steps based on NC feature unit, so as to improve the integration, visibility and controllability of CNC machining system. The definition of abstract NC feature unit and circumcision unit suitable for 2.5-axis machining are given. An algorithm of generating circumcision unit by link division method and tool path by circumcision unit is proposed.