In this paper

the basic system structure of the virtual NC(numerical control) machine tool is put forward and the basic conception of OOD(object oriented design) is introduced to the virtual system design of NC machine tool.Based on their respective characters

all parts of NC machine tool are classified into three classes: CStaticClass

CMoveClass and CDynamicClass.The STL files which containing the appearance feature of the undeformed objects are imported from solid modeling software(Pro/E) and feature modeling approach are adopted to describe the deformable objects

then combine with the respective animate functions to compose the classes

and finally accomplish the 3D dynamic simulation.The basic theory of quaternion is introduced and applied to the design of the system and the rotation of virtual NC machine tool.The methods provide a basic frame for studying on virtual NC system.The experimentations prove that the methods are feasible and have good practical value.