We give an approach on the detection and restraint of agent ability declaration deception in multi-agent system, and give a measure to detect and restrain the agent slandering and agent associated-cheat; we also give a method to recognize the agent impostor deception. Simulation test shows this method can fully detect the following impostor deception behaviors: an impostor falsely evaluates other agent; an impostor broadcasts rumor in other agent?s relationship web; an impostor cooperates with other agents. It provides a solution to detect and restrain agent deceptions in multi-agent cooperation.