This paper takes China’s 2013-2017 quarterly data of Internet financial development, small and medium-sized enterprises’(SMEs) development, small and medium-sized banks’ loan balances to SMEs as the research samples, and uses the unstructured vector autoregressive model-VAR(p) to make an empirical analysis of the promotion effect of small and medium-sized banks on the development of SMEs against the background of Internet financial development. The research results show that the development of China’s SMEs faces serious financing difficulties, but they have special advantages such as scale matching, low information asymmetry and strong business incentives in serving the financing needs of SMEs; therefore, small and medium-sized banks can effectively alleviate the financing constraints of SMEs by providing financial support to SMEs, thereby promoting the development of SMEs. In addition, the rapid development of China’s Internet finance in recent years has forced small and medium-sized banks to accelerate the process of reform and innovation, and thereby further strengthen the willingness and ability of their serving SMEs. However, in addition to the assistance of external financing channels and for sustainable development, SMEs have to rely on mainly their own accumulation, and in addition, the support of preferential policies of relevant government departments are also particularly important.