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 Miocene Yinggehai and Huangliu formations, the basin has gradually entered a stage of exploration, on which the medium-deep overpressured low permeability fields are focused. To address issues in the eastern margin of the basin, including relatively low exploration degree, unclear understanding of the characteristics of medium-deep reservoirs, and the genesis of high-quality reservoirs, the core and microscopic thin-section observations, logging data, and various types of analytical and test data were analyzed in detail. Eight major categories and 16 subcategories of lithofacies in the medium-deep layers of the eastern margin of the Yinggehai Basin were identified. The medium-deep sandstone reservoirs were found to be characteristic of "ultra-low porosity, ultra-low permeability, and dominance of secondary pores". Six diagenetic facies of medium-deep reservoirs and 23 comprehensive lithofacies-diagenetic facies types were classified. The mechanism of high-quality reservoir formation was dominated by secondary pores following specifically the rule of "reservoir control by dual facies, and pore preservation by overpressure and hydrocarbon charging". The theory on sedimentary-diagenetic exploration for medium-deep, ultra-low pressure and low-permeability reservoirs was improved, which provided a 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.