Abstract: During the process of injecting CO₂ into coal reservoirs, the diffusion and adsorption of CO₂ are slow process, and the adsorption and migration time characteristics under different injection pressures have a significant impact on the design of coal seam CO₂ storage. Therefore, dual energy X-ray CT scanning was used to calculate and analyze the changes of coal core density and CO₂ concentration before and after gas injection in coal reservoirs under confining pressure. The results show that in different regions of coal core, gas migrates at different speed conditions, and diffusion and adsorption progress are slow. The average CO₂ concentration in the coal core increases with the increase of time and CO₂ injection pressure, and the CO₂ concentration almost monotonically decreases along the axial direction of coal core from gas injection end to outlet section. The distribution of CO₂ concentration in coal core is uneven. The lower the CO₂ concentration in areas with high core density (mineral influence) is, the higher the CO₂ concentration in areas with low coal matrix density is.