We first discuss the universality and peculiarity of Marxism from the perspective of the Marx’s theory of system. We point out that the basic principle of socialist maturity is to develop production and achieve common prosperity. We then tentatively argue that mature socialism, based on the basic system of socialism, includes the economic, social and political elements and meanwhile creates other elements through top-level design. This is the underlying logic behind socialist maturity. This process essentially means that all the social premises for production are socialistic by nature and should follow their inherent law. In this way, these elements constitute the general system of socialism.