We conduct a survey of transformational towns and villages in High-tech Development District, Yaohai District and Shushan District, Hefei City. Using data, we analyze the "sideline effect" and inherent contradiction of transformational cities, research the policy needs for social security and its trend in the citizenization process of the peri-urban farmers. On this basis, we construct the social security policy system that can adapt to the accelerated process of urbanization. Finally, we put forth the following recommendations for the social security policy in the citizenization process of the peri-urban farmers: distinguishing different groups' policy needs for social security; attaching importance to people's dynamic policy needs for social security in urbanization; focusing on the adaptability of social security policy transformation in urbanization; attaching importance to the social psychosocial environment of social security policy transformation in urbanization; achieving the trinity of non-farm conversion, urbanization and citizenization in the process of urbanization; strengthening the government's dominant position in the building of social security policy system.