By means of X-ray diffraction analysis and environmental scanning electron microscope observation，the occurrence characteristics of dolomite and its relative abundance in shale drilled by Well Liye1 were studied to discuss the significance of relative abundance of dolomite on vertical sequence interfaces. Two kinds of dolomite in shale drilled by Well Liye1 were determined as euhedral dolomite and irregular microcrystalline based on their occurrence. Euhedral dolomite is characterized by two periods of recrystallization diagenesis，whose boundaries are similar to those of overgrowth rim；while irregular microcrystalline is characterized by origin dolomite. Dolomite in the shale drilled by Well Liye1 is a primary dolomite，part of which experienced the reformation of diagenetic recrystallization. The formation of dolomite can be divided into two stages. The first stage is the chemical precipitation of primary micrite and microcrystalline dolomite，and the second stage is the recrystallization through differential capillary pumping between laminae. It was proposed for the first time that the change of relative abundance of dolomite can be used as a typical marker for dividing the interface between the third and the fourth sequences of shale in the study area，which is corresponding to the high porosity reservoir. In the longitudinal direction，the closer the dolomite is to the sequence boundary，the higher the relative abundance of dolomite is，and the relative abundance of dolomite is lower when it is far away from the sequence boundary. The shale with high content of clay minerals developing at the upper of the fourth member of Shahejie Formation is characterized by high dolomite abundance.The content of illite developing at the lower of the third member of Shahejie Formation is relative low and the mixing content of illite/smectite is relative high，resulting in a high relative abundance of dolomite. It is indicated that the decrease of illite content and the increase of illite/smectite are favorable for the formation of dolomite.