At its beginning birth family contracts, carries political functions of social security as the transfer rules are subject to strict limits which different from other rural land contracting. Under the new historical conditions, urban-rural dualistic structure is in gradual deconstruction. Farmers are no longer dependent on rural land so that load gradually weakened the social security function of family contract. Subject to the system of family contracted period, families should be contracted “pure” as civil rights and do not need special circulation restrictions in order to meet the needs of rural economic development.