Two feature extraction methods for shape similarity based retrieval of 3D object models are presented. The proposed methods, which result in more effective and robust techniques for searching 3D models by similarity, support two essential query modes, namely, query by 3D model and query by 2D image. Our feature extraction scheme is inspired by observation of human behavior in recognizing 3D objects in practice. The process of extracting spatial arrangement from a 3D object surface and 2D shape features from projection images are achieved by adopting curvature distribution of the model surfaces and Fourier descriptors of the projection images.