Abstract: To analyze the performance of multi-body mechanical system at the preliminary design stage of virtual prototyping,the principle and methods to extract geometrical and physical attributes and topological structure of multi-body system from the tentative CAD model of parts and assembly design are presented. The topological structure of CAD model is mapped into a schematic diagram to serve as a visualized mathematical model for verifying its kinematic and dynamic performance.Comprehensive information for carrying out kinematic and dynamic analysis is acquired from the annotated CAD files of preliminary design.As a result,the virtual prototyping process could be completed quite successfully in a short time.A typical locomotive model is introduced to validate this approach.