Team work mode creates more achievements than individual mode in today＇s enterprises and thus becomes ever more popular. However, ethical crisis in the team, once emerges, will significantly affect group outcome. The leader contributes to the team＇s morality so much that ethical leadership has become an important research subject these years. To make clear how much an ethical leadership would affect on the group performance seems both theoretically and practically meaningful. Previous studies usually use social exchange theory to explain the interaction between an ethical leader and his team members. Two shortcomings commonly exist in such researches. First, they mostly focus on the behavior mechanism rather than the cognition mechanism, leading to the neglect over the analysis on and digging into the trust mechanism. Second, they neglected the necessary situational condition in the social exchange process, i. e. , only when the two parties follow the same moral protocols will they be able to follow the mutual favored rules required by the social exchanges. To solve these problems, this research constructs a theoretical model and conducts empirical studies in respects of the mediation mechanism and the marginal conditions of an ethical leader＇s influences on group performances. We firstly, based on four possible explanations, hypothesize that ethical leadership enhances group task performance. Secondly, we reveal the mediation mechanism by introducing trust perspective. According to social exchange theory, reciprocity will happen in a mature social exchange relationship, whereas mutual trust is the key to ensure that such responsibility will be fulfilled. On one hand, ethical leaders have behavioral consistency with his words and benevolence toward others. These characters will affect team members＇ trust towards ethical leaders. On the other hand, trust towards leaders will enhance interpersonal interaction within team and improve employees＇ working attitude, and ultimately improve team performance.