The practice of social security at all times and all over the world suggests that a reasonable definition of the government's responsibility in social security is the premise and foundation of a healthy and continuous development of social security. So it is made clear that the responsibility of government is the key to the building of a new social security system during the period of transition. On the basis of an analysis of the present conditions, problems and reasons of the government's responsibility during the period of transition, this paper holds that clearly defining the government's responsibility should follow five basic principles:sharing the government responsibility;separate design, supervision from implementer; unifying the right to financial arrangements and the right to routine arrangements;limitation and validation;combination of the officers and common people. By quartation method, that is separate according to different varieties, items, levels and ranks, this paper decides on the government's responsibility in social security and outlines its framework during the period of transition.