The original meaning of refers to the interaction among different components of the machine and the way of its operation.Social mechanism means the interaction among every parts of the society and the way of its operation,which consists of social level mechanism,social form mechanism and social functional mechanism.The social level mechanism mainly includes macro-level mechanism,meso-level mechanism and micro-level mechanism.The administrative-planned mechanism,guided-service mechanism and supervised-service mechanism are the basic categories of the social form mechanism.The promotion mechanism,guarantee mechanism and restriction mechanism compose the social function mechanism.The three kinds of mechanisms and their sub-categories have different connotations,but there are some internal and inevitable relations among them.The social mechanism,social Tizhi,social system and social principle are different categories but with internal and inevitable relations.It is helpful to make clear of the mechanism,understand the contents and regulations of mechanism reform and clarify the train of though of mechanism reform by exploring the theory of social mechanism.