In the era of big data, the service focus of commercial bank changes from large and medium-sized enterprises to large-medium-sized small and micro businesses and service content transfers from the traditional deposit and loan business to both online and offline. Also, the risk management changes from multiple varieties of risk management based on internal information to external change based on data integration. Firstly, this paper analyzes the impact of internet finance on commercial banks' business by big data. Secondly, it discusses the main reasons and development trend of commercial banks' strict control of small and microenterprise loans, and then discusses the risk management and control model based on big data. Finally it studies the path selection of the loan risk of small and micro enterprises in commercial banks. The result shows that: Commercial banks could provide service for small and micro enterprises with low cost, low risk and high return by new means of online e-bank, online loan inspection innovation mechanism, and investment loan linkage services. With the help of big data, the conditions for integrating small and micro enterprises' structured and unstructured data are already available, and credit risk can be controlled in a reasonable range.