This paper takes the deep sandstone of Bayingebi Formation in Guaizihu Sag of Yin’e Basin as the research object. Based on the basic characteristics of the reservoir, this article uses the constant rate mercury intrusion method to distinguish pores and throats and quantitatively characterize the characteristic parameters of pores and throats. Combined with scanning electron microscopy and casting thin section method, the morphological characteristics of pores and throats are qualitatively characterized, and the differences in microscopic pore structure are analyzed. In addition, different pore types are classified according to the fractal dimension of pore throat, and the main factors affecting the development of reservoir pores are discussed. The results show that the reservoir rock types in this area are mainly feldspar lithic sandstone with low compositional maturity. The average porosity of sandstone reservoir in the study area is 10.8%, and the average permeability is 1.17 mD, which belongs to low porosity and ultra-low permeability reservoir. Reservoir space types are mainly primary intergranular pores, dissolution pores and microfractures. The average pore radius is 195 μm, and the average throat radius is 3.5 μm. The pore structure types of the reservoir are divided into micro pore small throat type, small pore small throat type and large pore coarse throat type. The study area generally has the characteristics of relatively large pore-throat ratio, good pore-throat configuration relationship is an important factor affecting reservoir physical properties, and the main controlling factors affecting pore development are the combined effects of early diagenesis, organic acid dissolution and hydrocarbon filling. After relatively weak compaction and cementation transformation, the original debris provides a material and spatial basis for later dissolution, and the thick organic-rich mudstone at the top and bottom of the reservoir provides a source of organic acid dissolution and hydrocarbon filling.