To reveal the difference of the second member of Dongying Formation reservoir development along No.4 and No.2 tectonic belts in Nanpu Sag, the authors used such means as rock flakes, cast sheet image analysis, scanning electron microscopy, X-ray diffraction, mercury intrusion, physical property analysis and other data to study the reservoir characteristics systematically. According to the results obtained, the No.4 structural belt is mainly composed of lithic feldspar sandstone, the average debris content is Q_40.6F_30.1R_29.3, and the average component maturity is 0.69. The No.2 structural belt is mainly composed of feldspar lithic sandstone, the average debris content is Q_32.9F_26.8R_40.2, and the average component maturity is 0.49. The No.4 structural belt is mainly composed of low-permeability sandstone reservoirs, while the No.2 structural belt is dominated by tight reservoirs (permeability less than 1 mD). The sandstone reservoir space of the No.4 structural belt is mainly composed of primary residual intergranular pores, and the connectivity between pore throats is relatively good. In the No.2 structural belt, the sandstone reservoir space is also mainly composed of intergranular dissolved pores, but the connectivity between pores and throats is poor. The distribution of pore throat size of the second member of the No.4 structural belt is mainly unimodal, and the increase of mercury intrusion is mainly concentrated on the throat radius of more than 1 μm. The pore throat distribution of the No.2 structural belt is also mainly unimodal, but the increase in mercury is mainly concentrated on the throat radius of less than 1 μm. On the whole, the difference between the second member of Dongying Formation reservoir in the No.4 and No.2 structural belts in the Nanpu Sag is mainly the difference in microscopic pore structure. The reason for this difference lies in the difference between the sedimentary and diagenetic reformations of the Paleogene Ed₂ reservoirs of the two tectonic belts.