In order to overcome the defects of the traditional synthesis methods for rigid-body guidance mecha- nisms,such as the limitation of mechanism structure types and the uncertainty of functions,a generalized synthesis method based on the similarity transformation of mechanism function modules is proposed.In the method,first,by taking a belt mechanism as the objective,a kinematic analysis model is constructed and the output motion charac- teristic parameters are extracted.Next,the corresponding function module with full topology information is built.Then,by analyzing the intrinsic relationship between the mechanism parameters and the coupler rotation-angle function as well as that between the mechanism parameters and the guidance trajectory,the mapping rules between the guidance functions and the dimension parameters are revealed,and a method to preselect the reasonable dimen- sions of function modules is put forward.Finally,a fuzzy guidance motion design is introduced,and the geometric positioning of the mechanism function modules is accomplished through the center projective similarity transforma- tion,thus obtaining the actual dimensions and installation parameters of the mechanism.By a numerical example,it is proved that the proposed method is effective and applicable.