Abstract: In case-based design，the way of representing product model and product data structure have an important impact on the performance of case indexing and retrieval process．In this paper，we analyze the shortcomings of hierarchical structure，and build product model with extended entity-relationship（ EER） approach．A product model of fuel-pump is shown as an example．Four converting rules are applied when the EER model is converted into relational model． The main relational database and sub-case database can realize the function of searching both in attribute space and in function space．