Polysaccharide exists widely in the cell or cell wall of plant, animal, microorganism and epiphyte. As a kind of biologic substance having the action of immune regulation, it can enhance the function of both the nonspecific immunity and the specific immunity. The polysaccharide implements the regulation on immunity system by the following methods : stimulating the function of mononuclear phagocyte system, accelerating the proliferation of lymphocyte, promoting the level of antibody, inducing the exudation of cytokine, activating the complement system, and so on. In the international and domestic research, investigating on the actions of polysaccharide and its pharmacological functions is a primary goal. The pharmacological functions and the mechanism of the polysaccharide immune regulation are summanized.