With the rapid expanding of urban areas and with the accelerating urbanization process, the social insurance issue of land-lost farmers has become a big social problcm which is focused by the society today. Once the problem is not wellsolved, a series of social contradictions will be triggered because of this problem. This paper classifies the land-lost farmers into two types according to the cause of land-lost, one type is the farmers who are willing m leave the land and the other is the farmers who lost land because of expropriation of the land. The paper holds that the social insurance of the two type land-lost farmers should he treated differently to construct reasonable social insurance system for land-lost farmers.