How to solve the problems of social disadvantaged groups and concern their interests is a common task faced by the modern society. As the first cornerstone of social security system, social assistance system is of vital importance for solving the problems of the disadvantaged groups. In market-oriented economy, though deserved justice is necessary as an original distributive justice, it has some inborn limitations. The distributive justice value of social assistance system appears as the baseline justice which is accordance with the principle of demand, the principle of equality and the principle of share. Adhering to the baseline justice value of social assistance system is favorable for the unification of socialist equality and efficiency as well as the construction of a harmonious society.