As a subsystem of the society, community has its own systematic structure and law of movement.In this paper, the conception and the law of differentiating-combining movement of the community are given out on the basis of the system theory, and then the effect of the outside factors such as social factors, regional factor and neighboring community factor and the main content of differentiating-combining movement of the community are discussed.And in the third section, the special behavior of the law of differentiating-combining movement of the community in China is summarized.