A Pharos CAD system was proposed,in which the expert system and the parts family are adopted.The technique of the expert system based on RDBMS and the parts family structure were dis- cussed.The process of coding drive parameter computing and feature modeling was designed;and the problem of parameter transmission with respect to alterable structure CAD system was resolved.The system integrates the structure design,calculation,drawing,parameter optimization,process design and analysis,and realizes a parallel and rapid designs.