. Modular design technology is one of the ways to realize the product variety. It has been widely used in increasing fields. Module partition which has been the hot spot in and around the world is the key part of modular technology. In this paper, the combination of system clustering and the fuzzy ISODATA algorithm is used to achieve the rough-to-fine division according to the principles of module partition. Finally, the automobile security system has been taken as a case to justify the validity of the method and the result of the division accorded with the function of it.