Abstract: In the history of our party, MAO Ze-dong paid much attention to investigation and study. In different periods he made a large amount of such work in relevance. In addition, he gave the scientific expatiation to their importance, attitude and methods with the universal theories of Marxism. In the process of revolution and construction, the systematic and thorough theories concerning investigation and study gradually formed. In new period, it is of great practical significance to review MAO's such theories for proper understanding of the situation of our country, implementation of the spirit of the Third Session of the 18^th Congress of CPC, and completion of the mission endowed by the time to our party.