Abstract: Symmetry plane extraction is very important to the geometric model reconstruction of an object in reverse engineering. A mathematical definition of bilateral symmetry in point cloud is proposed after a profound study of the principle of symmetry, and an iterative closest point (ICP) based symmetry plane extraction method is presented. The method has been implemented in a reverse engineering software system RE-SOFT developed by Zhejiang university. The application in the reconstruction of an engine cover of a car and a sanitation part shows that the algorithm is capable of meeting the general engineering needs.