MAS (multi-agent system) is a sociality which is composed of many autonomy agents. Under the social background, realizing the goal of MAS depend on social rationality of agent. Although Jennings has presented a mode of social rationality, he doesn't obtain the method of computing socially rationality. In this paper, a new computed framework of social rationality is constructed based on the principle of synergetic and point the physical significance of parameters. The authors shell parameter's computing divide into four steps; approximate liner, define order parameter; built differential questions and solve to it.