The social commitment between agents needs to be built for problem solving in the multi-agent systems. A mechanism of social commitment by combining Belief-Desire-Intention and Utility theory is presented in this paper, which guarantees agent's rational action on logic and decision. The Rao & Georgeff's Belief-Desire-Intention theory and S.Kraus's idea of incentive contract are combined ,the Haddadi's mechanism of social commitment is modified, and the Castelfranchi's concept of social commitment with implementing support is provided in this paper.