Abstract: Luhmann’s thoughts on the sociology of law can be divided into the early thoughts and the late thoughts. His late thoughts on the sociology of law is usually considered to represent his ideas in the mature stage of his theory, so they have been widely spread and used for reference around the world. In contrast, Luhmann’s early sociological theory of law is generally neglected. Actually, it has irreplaceable theoretical value and enlightening significance. Luhmann’s early sociological theory of law consists of two parts: content and method. In terms of content, its greatest contribution is the unique sociological description of legal norms, and the elaboration of the theory of co-evolution of legal system and society from the perspective of neo-Darwinian evolution theory. As for the method, the concept of constructing meaning, which is the mechanism and basis for the co-evolution of consciousness system and social system, the comparative method of equivalent functionism and the general system theory of phenomenology are the features and contribution to the methodology of Luhmann’s early sociological theory of law.