This paper takes the degree of debt concentration and product market competitive advantage as intermediary variables to explore the internal mechanism of the impact of CSR fulfilment on firm debt risk. It is found that the fulfilment of CSR can reduce the debt risk of firms by dispersing the degree of debt concentration and enhancing the competitive advantage of product market. The mediating effect of the degree of debt concentration has a direct impact on the competitive advantage of a product market and is particularly obvious in private firms and firms in the eastern region of China.