An ontology based data description norm of web parts library was proposed. With the help of parts family and article characteristics table, the framework was built to solve the problem of parts data sharing and reusing. The generic and simple parts family was used to build the hierarchy and the article characteristics table was used to store the information of parts instances. Through the expansion of ontology library, CAD template and article characteristics table of parts, the dynamic expansion of web parts library was realized. A multilevel query model was brought out, and vertical and horizontal matching was used to deal with the problem of query precision. A prototype of ontology based on web parts library was constructed to verify the feasibility of above methods.