This paper takes A share listed companies in Shanghai and Shenzhen from 2013 to 2018 as the research sample, and reveals the influencing factors and mechanism of board informal hierarchy on M&A performance in China. The results show that the clearer the board informal hierarchy is, the better the long term M&A performance is. In terms of influencing factors, when the environmental uncertainty is higher and the equity concentration is lower, the positive impact of board informal hierarchy on the long term M&A performance is more obvious. In terms of influential mechanism, board informal hierarchy can restrain managers self interest behavior and restrain managerial overconfidence, so as to improve the long term M&A performance.