The physical properties of Chang 8 oil reservoir are controlled by clay mineral cements, and the sedimentary process and diagenetic changes in the late sedimentary period determine the present appearance of the reservoir. The basic characteristics of the reservoir, diagenesis and sedimentation were analyzed by means of cast thin section and scanning electron microscope. Under the background of overall low permeability, some oil Wells located in the relatively high permeability area had higher production, sorted out the enrichment law of Chang 8 reservoir in the study area, and analyzed the factors of rock porosity decline in the area. In Jiyuan area, there are many underwater distributary channels and estuarine bar deposits in favorable reservoirs, especially in the central part of the sand body, the reservoir properties and seepage properties of Chang 8 oil formation are good, namely, intergranular porosity, intergranular porosity + solution porosity and solution porosity + intergranular porosity. The percolation performance of dissolved pore type, intergranular pore + micropore type is poor. The reservoir space of micro-porosity and dissolved porosity + micro-porosity is mainly composed of micro-porosity with small radius, poor connectivity, poor pore surface area and seepage resistance, and poor reservoir and seepage performance.