Abstract: First,the sub-part,which is to be retrieved,of a 3D CAD model is selected interactively by users and its attributed graph is automatically generated.Second,for each CAD model in the database,surfaces that are similar to those of the chosen sub-part are identified.Then,other irrelevant surfaces are deleted from the model's attributed graph.Thus,the parts that are possibly similar to the sub-part are separated from the model.A method for calculating the similarity coefficient of the separated parts and the sub-part,which uses a optimal matching algorithm for bi-graphs,is proposed.Experimental results show that this algorithm can efficiently achieve partial retrieval.