The system of people’s congress is the fundamental political system in our country and the basic norm commonly established by the “Common Program” and the four official constitutions after the foundation of China. The socialist constitutional legal system is the structuralization and systematism of the basic norm. Although the political practices can obstruct and even weaken the effect of the constitutional legal system，they cannot abolish the basic norm and its legal system in accordance with the principle of legality. The division of the three phases of the starting points of history，practice and logic of our socialist constitutional legal system further explains the uniqueness and continuity of our socialist legal system since the foundation of China，presents the standardized reason of our constitutional legal system in the whole socialist construction and the early period of the reform and the openness. The continuity between the legal system thirty years before the foundation of the new China and that thirty years after the foundation of China is larger than the break between them，and the principal line connecting these two is the basic norm of the system of people’s congress，which is the situation to which we have to pay attention when understanding our socialist constitutional legal system and only from the angle of epistemology of law can we explain the topic of legality of state continuity.