Abstract: In terms of problem consciousness and basic position, the internal coherence between Luhmann’s earlier and later researches on the sociology of law is far greater than their differences. The study of the function of law and the positivism of modern law run through Luhmann’s academic career. In the early stage, Luhmann defined the function of law as the stabilization of normative expectations from the perspective of system theory with the help of the “Husserl+Parsons” model and the research methods such as function analysis, meaning analysis, system analysis, and decision analysis. At the same time, Luhmann regarded legal positivism as the historical evolution process in which the legal system comprehensively coordinated the contradiction between “learning and non-learning” to overcome the increasing complexity and contingency of society, thus improving its structural adaptability.