For the successful realization of product configuration design (PCD) in the condition of mass customization mode, the module encoding methods are studied. By analyzing the product structure model and the process of computer-aided PCD, all related information which is required for the module is decided. This paper proposes a scientific module encoding method suitable for PCD. It describes the geometric features of the modules, the interface relationships and the affiliations between modules. Further more, it introduces additional attribute codes used to evaluate product configuration. By this way the product information can be fully expressed in order to improve the efficiency of PCD.