Corporate tax avoidance brings massive impacts to a country’s fiscal revenue, which also undermine the market fairness. Using the data regards Shanghai and Shenzhen A-shares from 2009 to 2020, we found that with the increase of customer concentration, firms are likely to engage in more tax avoidance activities. Further researches reveal, for non-state-owned enterprises, small enterprises and enterprises with high product uniqueness, the positive correlation between customer concentration and corporate tax avoidance extent is more obvious, simultaneously, the regression results are still significant in the robustness tests. Moreover, three mechanisms that customer concentration affects corporate tax avoidance are determined in this paper. They are corporate profit compensation, financial constraints and external supervision.