Abstract: In order to meet the requirements of real-time retrieval of large-scale part library and reusing structural unit of part models, a 3D part model retrieval method based on surface region decomposition is presented. The planes are divided into convex boundary plane, concave boundary plane and mixed boundary plane. The curvatures of boundary neighbor domain, perpendicular boundary and border boundary are introduced to define the boundary concavity of the surface. The condition that saddle surfaces are regarded as convex, concave or flat surfaces in analyzing region concavity is presented. Based on whether or not the region concavity is changed after merging two surfaces, the edge classification specification is presented. By outer edge closing specification, undetermined edge transformation specification and flat region merging specification, surface region decomposition of 3D part models is realized. Surface region code specification is used to code the decomposition region. By use of region structure codes, the retrieval mechanism of the similar parts is presented. Experimental results show that global structure retrieval is more effective after region decomposition, partial structure retrieval can be realized by intersecting operation of dual adjacent regions.