Abstract: The significance of complex product systems innovation and the important role of complex product systems in national economy are introduced. And then, the innovation difficulty of complex product systems is analyzed in detailed. Furthermore, the innovation flow of complex product systems based on modularization development is brought out. At last, the particular argumentation about what the innovation flow of complex product systems based on modularization development according to the city underground traffic control system is carried through.

Key words: complex product systems, modularization development, innovation flow, case investigation