Based on the data of listed fims in the A-share of Chinese stock market from 2008 to 2016, this paper first examines the relationship between the Chinese BIG 10 audit firms and corporate tax aggressiveness, and further analyzes the moderating effect of outside institutional environment. The results show that"BIG 10"is negatively related to the degree of corporate tax aggressiveness, indicating that domestic large firm's audit has inhibitory effect on corporate tax avoidance as an effective external supervision.A further study finds that "BIG 10"is more likely to restrain corporate tax aggressiveness when the law level is high or the government intervention is low, which reflects that the improvement of legislation level and the reduction of government intervention helps to strengthen the supervision function of the independent audit.