It analyzed the substance of parametric design. Nowadays, the CAD technology can not express the product knowledge and design experience. The combination of knowledge-based engineering (KBE) and CAD solved these problem in the filed of molding. UG/KF is a new technology to integrate CAD and KBE. This paper develops the mould parts with UG/KF as an example to explain its application, and point out the developing direction of CAD by analyzing new characteristics of knowledge fusion.