Abstract: Adsorption characteristic of supercritical CO₂ on coal directly determines the CO₂ geological storage capacity. Through volumetric method, this paper analyzed the manifestation effects of different models on the experimental data of various ranked coals and activated carbon. The results indicate that the variation rate of gaseous CO₂ density reaches the peak around 8 MPa. Introduction of parameter k could improve the fitting quality and trap various experimental errors. The adsorption mechanism of coal samples from Tiefa and Wolonghu is micropore filling. As coal samples of Yaojie is collected from a CO₂ -rich reservoir, the alteration effect by experimental CO₂ adsorption is unobvious and its micropores develop quite well, thus the greatest absolute adsorption is higher than other samples. When the gas density increases gradually, the gap between excess adsorption and absolute adsorption widens, and the absolute adsorption determines the adsorption capacity of the coal samples. The fitting CO2 adsorbed phase density of the activated carbon by OK model is 1.004 g/cm³.