The level of social security reflects the extent to which people share the fruits of economic and social development，and relates to sense of happiness，gain，and security of capital residents. Taking 16 districts of Beijing as the research cases，this paper constructs an index system of social security level from three aspects of expenditure level，coverage scope and security intensity，and then evaluates the evolution and regional differences of social security level for 16 districts. Furthermore，the main factors that affect the improvement of social security level are identified. The results show that the social security level in 16 districts has been improved from 2010 to 2019，and the level and growth rate of urban areas are generally higher than peripheral areas. The primary obstacle factor has undergone a change from the security intensity index to the expenditure level index. Combined with the problems identified and future planning，some policy suggestions are proposed in the final part.