Abstract: Injecting CO₂ into gas reservoirs to enhance gas recovery, known as CCUS-EGR (Carbon Capture, Utilization, and Storage for Enhanced Gas Recovery) technology, is poised to become the key technology supporting the strategic goals of the "dual carbon" target. To address the unclear mechanism of CO₂ injection for enhancing gas recovery in conventional and tight gas reservoirs, experiments about the permeability of rock samples under different temperatures and pressures were conducted to determine the CO₂ permeability across different phase states. Micro-scale numerical simulations were employed to compare the extraction efficiency, sweep efficiency, and displacement efficiency of CH₄ when injected with different media in pore spaces. Additionally, CO₂-water-rock reaction experiments were performed on samples of various rock types containing bound water, with changes in permeability and pore structure of gas reservoirs before and after CO₂ injection assessed using NMR (nuclear magnetic resonance) equipment. The research results reveal that supercritical CO₂ exhibits viscosity similar to gas and density close to liquid, along with exceptionally high permeability. Compared to N₂ and H₂O, CO₂ demonstrates the highest diffusion coefficient, the greatest micro-scale sweep efficiency for CH₄ in pore corners, the most effective displacement performance, and consequently, the highest CH₄ recovery rate. The CO₂-water-rock reaction results in the densification of carbonate rocks, tight sandstones, and volcanic rock samples, accompanied by a reduction in bound water content. Among these, carbonate rock samples exhibit the most intense reaction, with an increase in macropore vo-lume proportion post-reaction, whereas tight sandstone and volcanic rock samples show a decrease in macropore volume proportion. Ultimately, the permeability of bound water-containing rock samples is governed by the extent of mineral precipitation and the reduction in bound water saturation. This study provides theoretical support for the pilot test of CO₂ injection in conventional and tight gas reservoirs, offering valuable insights for field applications.