To better understand the mechanism of interactions of supercritical CO2 (SCCO2) and H2O, untreated, SCCO2 treated and SCCO2-H2O treated anthracites were adopted to analyze changes in pore structure, adsorption capacity. Observations from experimental data reveal that mineral and other substances in the fractures and matrix of coal body are dissolved and mobilized by the carbonic acid formed from the mixture of SCCO2 and H2O, which may contribute to smaller pore development and enhance the adsorption capacity. These findings may provide new insights into effective and safe storage of CO2 in coal reservoir.