The financing problem of SMEs in China has caused widespread concern. Based on the wind database, this paper uses the hierarchical linear model to examine the impact of enterprise size and banking structure on the credit capacity of SMEs, and introduces commercial credit environment variables to study whether the impact will change under different commercial credit environments. This study found that the larger the enterprise size and the more dispersed the banking structure, the stronger the credit capacity of the SMEs. But the impact is weakened with the improvement of the commercial credit environment. This study can be great reference in improving the credit capacity of SMEs.