Innovation has become increasingly important in the transformation of China's economy and the gradual intensification of fierce external competition. Due to the high risk of R&D investment and the asymmetry of information, companies are still difficult to obtain the required debt capital. Compared to external indirect financing, commercial credit has become a low-cost, high-efficiency financing channel as it is directly linked to commodity transactions and allows the two sides to installment and prepayment. On this basis, this paper tries to test the relationship between financial support, commercial credit and heterogeneous R&D investment by empirical test, so as to find a channel to resolve the capital crisis. The results of this paper first confirm that cash flow generated by listed companies is one of the important capital sources of R&D investment. Secondly, after controlling the cash flow, scale and R&D investment tendency, financial development has significantly strengthened the scale of R&D expenditure, and the higher the degree of financial development, the smaller the impact on the R&D investment. In the separate relationship study of financial support and commercial credit for R&D, the result shows that they both are important sources. In addition, there is a complementary relationship between financial support and commercial credit in commercial banks, but theres is a difference in the support of commercial credit for heterogeneous R&D investment.