Aiming toovercome thelimitation of the traditional design methods of automobile parts, this paper presents a design and analysis method based on "Soft Prototype". By developing a professional CAD system Drum Brake Design and Analysis System, the authors researched the design method of "Virtual Products" and the technologies of parameterized modeling. During the development of software, some new methods are presented. In this CAD system, the database, graphical browser and designing module are united perfectly, and parameters are utilized to create models. Such a system can greatly improve design efficiency and reduce the time of new products development