Abstract: The application of data base techniques in computer-aided design of dies and molds is presented in this paper. A hierarchical data model, called "locating tree" and suitable for the computer representation of dies, molds and other mechanical structures, is used to describe extrusion Sies which are the design object of a die CAD system. Based on the hierarchical data model, the conceptual design, logical design and physical imple mentation of the CAD data base system for extrusion dies are conducted.