In this paper a novel method of representation and retrieval of 3D CAD models in part libraries is presented with the aim being to facilitate the reuse of parts. Firstly, we analyze the basic principle of voxelization, compare several existing algorithms for voxelization and choose the most appropriate one to approach the original CAD model. When the 3D model has been voxelized, it is composed of a certain amount of voxels in the same size. Then the voxelized model is divided into several subspaces, and the entropy of each subspace is calculated. Finally, all of these entropies constitute a feature vector which represents the model when compared with other models. This algorithm is a content-based method, so it only relies on shape and does not need any semanteme or coding information, which simplifies the process of analysis. An archetypal system based on this idea is implemented and its feasibility obtains preliminarily validated.