A KBS (Knowledge Based System) based on CATIA (Computer Aided Three dimensional Interactive Application) for aircraft assembly-design is developed by using Oracle database management system and Visual C++. Net and CAA (Component Application Architecture) FOR CATIA V5 and the structure, implementation method and key technologies are anylized. The integration of system user interface and CATIA software environment posesse interactivity, which achieves tapid reuseing of knowledge and experiences, asisted learning, rapid design, as well as effi ciency improving.