The Bohai Bay Basin is one of the important hydrocarbon-bearing basins in eastern China,and its complex reservoir-forming characteristics are closely related to modification by deep CO₂ injection and CO₂-rich hydrothermal activity. A comprehensive analysis of the correlations among CO₂ content, δ¹³C_CO2, and R/Ra indicates that the CO₂ in the basin is primarily derived from CO₂ released by deep mantle-derived magmatic activity. Statistical analysis of CO₂-bearing fluid inclusion data reveals a bimodal pattern in homogenization temperatures, suggesting that the study area reservoirs have undergone multiple episodes of hydrothermal modification. Additionally, this study summarizes various lines of evidence from petrology-mineralogy and geochemistry regarding the impact of hydrothermal activity on reservoirs. Petrological-mineralogical evidence includes typical hydrothermal minerals such as ankerite, pyrite, chlorite, and dawsonite. In regions like the Bozhong Depression, Jiyang Depression, calcite in reservoirs exhibits lower oxygen isotope values and positive Eu anomalies in rare earth elements,indicating a hydro- thermal origin. The modification of reservoirs by deep hydrothermal fluids shows significant spatial differences. Near areas of deep hydrothermal activity, CO₂-rich hydrothermal fluids significantly improve reservoir porosity and permeability through dissolution and thermal baking effects, with the peak of dissolution-induced improvement occurring at the leading edge of hydrothermal activity. In contrast, in areas far from deep hydrothermal activity, precipitation and cementation of authigenic minerals (e.g., dolomite, calcite, quartz) lead to reduced porosity and permeability.