Abstract: The changed practice needs the developing guiding theoretical guide and promotes the constant innovation of theory.The important thought of "Three Represent's" came into being because of the changes of the world situation,the national situation and the Party's situation.Like Mao Tsedong thought and Deng Xiaoping's theory,it has inherited Marxism and developed the spirit of keeping up with the times,making Marxism localized in China.With a series of new thought,new viewpoint and new thesis,it further deepens the realization of the two basic theories of "what is socialism and how socialism should be built" and "what party should be built and how it should be built",thus initially forming the new theory system.