It is important for having the initiative in competition to infer the rival's private information accurately. In this paper, the rival's decision making model is described by influence diagram. According to the criterion that rival is apt to gain the global maximum expected utility rather than to gain the local maximum expected utility, we infer rival's private information about cost, bankroll, tactic, and utility by combining decision computation and Bayesian network illation. The experiment results show that our proposed method is feasible.