The classical economic theories and models provided analysis basis and tools for modern study on the rural-urban dual labor market in developing countries.Based on the idea of Harris-Todaro model,we construct a more predigested model,which can integrate many problems to analyze,such as farmer inbursting city,unemployment in city,rural-urban income disparity,social inequity(Gini index) and so on.Using Lorenz-curve,the choices and effects of government policies in integrating rural and urban development,especially the science logic of "developing rural economy,increasing farmer's income",can be expounded clearly.