Small and micro enterprises underpin China’s economic growth，but the problem of difficulty and high costs in financing has become a major obstacle for the development of small and micro businesses. Recently，policies are introduced and financial institutions are asked to support small and micro businesses. This article concludes the causes of small and micro enterprises’ financing difficulty，and introduces the principles of financing small and micro businesses for financial institutions. Also，this paper analyses the difficulties for trust to involve small and micro financing，and discusses possible solutions and business patterns.