The key technology of design and implementation of CAPP system for extrusion casting of automobile parts based on knowledge was studied by using auto parts as the research object and extrusion casting process planning knowledge. The framework of the auxiliary process planning system based on knowledge was introduced. Then the establishment of the knowledge base of CAPP system, the representation and mapping of knowledge, the reasoning strategy and the running mechanism were discussed further. The implementation of CAPP system was discussed based on the modeling method of feature object.Finally, the implementation process and method of the CAPP were analyzed with the engine shell as the example.In the whole CAPP system, the knowledge of extrusion casting and the intelligent generation process through the internal reasoning strategy were integrated. The automation and digitization of the extrusion casting of automobile parts were realized, greatly shortening the time of process planning.It can solve the problems of inefficient, difficult to guarantee the correct rate and information is not easy to share in traditional manual way.