In China, A great deal of farmers' land are expropriated by local government in the process of urbanizaion, These peasantry of lose their land not only lack of employment opportunity in city's industry and service department, but also lack of social security. How to ensure the rational benefit of lose land's peasantry and stipulate for rational compensation for this peasantry in the process of Urbanization ? This paper aims at this problem, analysis the theory base of "Land Trade Security",and analysis the structure of rational benefit of lose land's peasantry, in the end, this paper points active meaning of Shanghai's "social security model of small town",and also puts forward some suggestions to perfect the "social security model of small town ".