In this study,according to the changes of curvature of the outline and the partial shape center location of the irregular object,a mathematical method is set up to build up the3D model of the irregular object,which is a solid foundation to analyze and design the object.This method,which has successfully built up mandible3D model,one of the most complex parts of the body,and made mechanics analysis,has been applied in the clinical engineering and also gives some idea to analyze and design complex parts in other fields.