The Upper Permian Longtan Formation in the Lower Yangtze Area is rich in oil and gas. Preliminary industrial oil flows have been obtained in recent years, although significant exploration progress remains elusive. In order to provide a comprehensive analysis of the development characteristics of the Longtan tight sandstone reservoirs in the Lower Yangtze Area and to explore the formation mechanisms of high-quality reservoirs. A systematic investigation of the mineral composition, diagenesis, and reservoir characteristics of the Longtan sandstones was conducted using various experimental methods, including core observation, thin-section analysis, X-ray diffraction, cathodoluminescence, scanning electron microscopy, energy-dispersive spectroscopy, nuclear magnetic resonance, imaging logging, and fluid inclusion analysis. The results indicate that the tight sandstone reservoirs are primarily shaped by diagenetic processes such as compaction, cementation, and dissolution. Compaction and cementation contributed to reservoir densification, while dissolution was the principal constructive diagenetic process. Alternating acidic and alkaline diagenetic environments promoted the dissolution of feldspar and quartz, leading to cumulative effects on the reservoirs. The overall diagenetic evolution occurred during the mesogenetic stage. Reservoir porosity was predominantly developed at the nanoscale, with secondary intragranular pores and microfractures being the dominant pore types, whereas primary intergranular pores were less developed. The characteristics of paleo-reservoirs filled with light oil bitumen and the microscopic features of fluid inclusions, suggest substantial multiepisode hydrocarbon charging and accumulation processes in the Longtan Formation. The Huangqiao onshore region of the Lower Yangtze Area and the Laoshan Uplift in the South Yellow Sea Basin, both located in relatively tectonically stable regions, exhibit more pronounced dissolution-enhanced porosity in the Longtan Formation tight sandstones than in other areas, indicating promising exploration potential.