Abstract: Corporate debt conservatism is one of the frontier issues in capital structure theory. Based on the theory of implicit contract, this paper analyzes the influence mechanism of customer concentration on the debt conservative behavior of Chinese A-share listed companies in 2007-2015, and explores the alternative role of internal control in the implementation of implicit contract in debt conservative policy.The empirical results show that the higher the customer concentration is, the more likely the enterprise is to adopt conservative debt policy, and the positive correlation between customer concentration and corporate debt conservatism is more significant in durable goods manufacturing enterprises, which shows that the enterprise can transfer its future performance ability to customers by choosing conservative debt policy;with the improvement of the quality of internal control, the positive correlation between customer concentration and debt conservatism becomes weak, which indicates that internal control and debt conservatism have a certain alternative role in the implementation of implicit contracts. The above conclusions enrich the explanation of the conservative causes of corporate debt, and have a certain reference significance for enterprises to deal with the relationship with customers and other supply chain stakeholders.

Key words: capital structure theory, implicit contract, customer concentration, debt conservatism, internal control