The notion of "the Party's leadership system" was first proposed in the Fourth Plenary Session of the 19th Central Committee of the CPC, whose great theoretical and pragmatic significance should be understood and maintained from four perspectives,i.e. connotation, precondition, assurance and theory.From the perspective of ideological connotation, the Party's leadership system has been reflected in four aspects: Party's leadership, institutional system, formation of system, innovation in development.From the perspective of fundamental precondition, the Party's leadership is the political assurance of the formation of socialist political system with Chinese characteristics. From the perspective of political assurance, the Party's leadership is the fundamental assurance of exploiting the advantage of socialist system with Chinese characteristics. From the perspective of theoretical development, the notion of "the Party's leadership system" can be taken as the development of Marxist theory of political party and state construction.Understanding the great significance of the notion of the Party's leadership system comprehensively contributes to understanding the important role of socialist system with Chinese characteristics in the modernization of the governance system and capabilities.