After neo- structuralism raised the problem of financial structure of developing countries, scholars have developed a lot of theoretical and empirical study on financial dualism, Based on the opening character of the theory, this paper uses the probit model to examine the operations of formal and informal finance in chinag rural areas, analyses the factors that induce farmers to borrow from formal or informal finance, and explains the theoretical reasons for the existence of rural financial dualism as a system on the basis of microcosmic.