Abstract: Identification of the CO₂ adsorption/desorption characteristics in coal and rock under supercritical conditions can provide theoretical basis for in-situ CO₂injection parameters. Taking the lean coal in Tunliu mine and anthracite in Sihe mine as the research object, by means of ISO-300 isothermal adsorption experiment instrument, the adsorption/desorption experiments in different temperature (35℃, 45℃, 55℃) were conducted with the maximum pressure above the critical pressure of CO₂. The results show that under supercritical conditions, with the pressure rise, the adsorption capacity by capacity testing methods is of the maximum value, not represents the absolute adsorption, but is the adsorption of Gibbs. According to the essence of CO₂ adsorption in coal and rock under high pressure, the real adsorption and desorption capacity under supercritical conditions were calculated. The relation between real adsorption capacity and pressure are accord with Langmuir adsorption curve, with the adsorption pressure rise, the difference values between the adsorption capacity of Gibbs and absolute adsorption capacity increase. With the temperature increase, the adsorption capacity is reduced. The adsorption capacity of anthracite is greater than the lean coal in the same conditions. The absolute adsorption isotherms and the absolute desorption isotherms under supercritical state of co₂ are reversible.