In this paper, the macroscopic and microscopic features, diagenesis and origin of microsparite (molar-tooth) carbonates of Dalongkou Formation have been analyzed based on various kinds of technical methods, such as EMPA, SEM and EM. The results demonstrate that microsparite calcite can exist in the substrate in three forms: it can be distributed disorderly in the micrite, or it serves as the equal-grained microsparite assemblage filling in the general molar-tooth structure belt, or it can act as the cement between the ooids, intraclast, and algae aggregate composed of microcrystal calcite. This paper has also interpreted the reason why the molartooth structures with wide middle part and tip end point appeared.