It is an important subject to build the model of mental states for Agents in the theoretic research of agent. A model BDICU ( belief desire intention combined with utility) of mental states combined with ut ility is presented in this paper, which guarantees agent's action with rational logic and decision, the problem of side effect with a solution is provided, and the rules for producting and updating goal and intention are also presented. Thi s model modifies and extends Rao and Georgeff's Belief-Desire-Intention theory , and provides rational agent systems with implementing support on logic and utility.