Abstract: This paper analyzes the difficulties of basic primitives current of geometrie modeling systems, which are encoutered in the application of NC machining. On-the basis of the analysis, the paper proposes the primitive design rules for the integrated CAD/CAM systems. The paper is divided into .four parts. The first part analyzes the defects of conventional primitives, the second part discusses requirements of primitive in the integration of CAD/CAM and proposes a unified method of desig ning primitives, the third part introduces sweeping solids constructive principles, and the last part provides an example to show the advantages of the method.