The rational man hypothesis is one of cornerstones of economics mansion. Since its being proposed, it has received wide and fiercely criticism by Scholars. But it did not seem to impede the individualism analysis method that was based on the rational man hypothesis branching out, and to form into the huge economic imperialism. Until now, it also didn’t seem to slow down the pace of aggression. Behind appearances, it must have the reality needs of the rational man hypothesis, and the intrinsic rationality and important value. Firstly, rational man hypothesis is a kind of methodology logical that is necessary for scientific research. Secondly, the rational man hypothesis is to pursue of maximizing, rather than to maximize, and whether the dream realization can realize depend on system, technology, culture and other reality. Moreover, compared to other human nature assumption, it is closer to reality and provides a possible approach for the social governance. Finally, it is the precondition of incentive constraint system design.