To better actualize product's modular design, the clustering algorithm based on graph partitioning for product's conceptual elements was introduced into the process of product's conceptual design on basis of FBCS (function，behavior，conceptual structure), and a FBCS-based method for product's conceptual module identifying was presented. Stacker's push-puller is taken as a type example while the method of product's conceptual design was analyzed. The method achieved the iterative transforming form function to behavior，form behavior to conceptual structure，form conceptual structure to sub function according to the product's general technology characteristic. To describe the conceptual product，the conceptual product's modeling method which combined black box with function description of IDEF0 was presented to construct the product's function-conceptual structure model. Then，the correlation analysis approach of product's conceptual elements (function，behavior，conceptual structure，interface) was established. To realize the identifying of product's conceptual module，the clustering algorithm based on graph partitioning was adopted to converge product's conceptual elements. This method was proved to be feasible and effective by identifying of the push-puller's conceptual module.