Abstract: With the increasing exploration degree in mature areas such as the Dongfang Area and Ledong Area of the Yinggehai Basin, as well as the main stratigraphic series such as the Yinggehai and Huangliu Formations, the basin has gradually entered a stage mainly focused on the exploration of the medium-deep overpressured and low permeability fields. Aiming at addressing issues in the eastern margin of the basin, such as relatively low exploration degree, unclear understanding of the characteristics of medium-deep reservoirs and the genesis of high-quality reservoirs, a systematic study was conducted based on core observation, microscopic thin-section identification, logging data, and various types of analytical and test data. The key findings of the study are as follows: identified 8 major categories and 16 subcategories of lithofacies in the medium-deep layers of the eastern margin of the Yinggehai Basin; Clarified the basic characteristics of medium-deep sandstone reservoirs, namely "ultra-low porosity, ultra-low permeability, and dominance of secondary pores"; Classified 6 diagenetic facies of medium-deep reservoirs and 23 comprehensive lithofacies-diagenetic facies types; Revealed the formation mechanism of high-quality reservoirs in the medium-deep layers of the eastern margin of the basin, which are dominated by secondary pores and follow the rule of "reservoir control by dual facies, and pore preservation by overpressure and hydrocarbon charging". From the perspective of sedimentary-diagenetic theory, this study improves the research system for medium-deep, ultra-low pressure and low-permeability reservoirs, with the expectation of providing theoretical support and technical guidance for exploration breakthroughs in the medium-deep, ultra-low pressure and low-permeability fields of the eastern margin of the Yinggehai Basin.