<p>This paper takes the Chang8 reservoir of Yanchang Group in Yanchi area as the research object, aiming at revealing its sedimentary microphase and reservoir characteristics, and providing scientific basis for oil and gas exploration and development. The distribution characteristics of the sedimentary microphase and the physical characteristics of the reservoir are systematically studied by using field geological profile, drilling core, well logging and experimental analysis. The results show that the sedimentary microphase of the reservoir of Long 8 Formation Group mainly includes submerged diversion channel, submerged natural dyke and diversion interbay, etc. The average thickness of seepage sand layer of submerged diversion channel phase is 20.3 m, and the average value of sand- ground ratio is 0.53, among which, the type of sand formation of the submerged diversion channel phase is a double-segment II type curve characterized by the combination of heavy jumping component and fine-grained suspended component, showing good pore connectivity. In terms of reservoir characteristics, the Chang8 oil formation shows low porosity (10.83% on average) and extra-low to ultra-low permeability (0.776·10^-3 μm² on average), with intergranular pores and feldspathic pores dominating the pore structure, and feldspathic pores accounting for 55.42% of the total pores, and there are a small number of clastic pores, intergranular pores, intergranular pores, and microcracks, which reflect the influence of diagenesis on the reservoir material. These characteristics reflect the significant influence of diagenesis on the physical properties of the reservoir. This study provides an important geological basis for the exploration and development of Yanchi Yanchang Group Long 8 reservoir, and helps to optimize the reservoir development plan and improve the recovery rate.</p>