Abstract: The sorption properties of coal associated with carbon dioxide under different gas pressures were studied by X-ray CT technology and strain measurement. It is found that coal strain increases as time goes and gas pressure increases, with different values along different directions, and gas sorption leads to increase in coal porosity; Both the average value and standard deviation of gray of coal CT image manifest an increasing tendency as time goes and gas pressure increases. The results show that coal swelling deformation occurs after it adsorbs CO₂, which provides more surface area for adsorbing more gas and induces increament in density of coal-gas mixture; the effect of average density increase caused by matrix adsorbing gas is larger than the effect of average density decrease caused by matrix volume expansion; and gas sorption results in the aggravation of heterogeneity of substance distribution inside the coal.