Abstract: In order to reveal the adsorption characteristics of different gases in the coal slit pores, the adsorption behaviors of CH₄ and CO₂ in the coal slit pores with equal proportions at different temperatures and different pore sizes were studied by using the giant canonical ensemble Monte Carlo simulation method. The results show that the isothermal adsorption curves of CO₂ and CH₄ by coal slit pores are consistent with the Langmuir adsorption theoretical model; the adsorption amount and heat of CO₂ are greater than that of CH₄, the adsorption amount of coal slit pores decreases with the increase of temperature, but the adsorption amount is less affected by the adsorption heat; the adsorption of CO₂ and CH₄ by coal slit pores is a thermodynamic spontaneous process, and the change of the adsorption heat range is small under different pore sizes; the entropy change is less than 0, indicating that the movement of gas molecules adsorbed on coal is limited, which leads to the decrease of the chaos of the whole system and the less easy the adsorption process; in the adsorption process, the van der Waals force is the main force, and the molecular electrostatic force is the secondary force, both of them decrease with the increase of pore size. The van der Waals potential energy and molecular electrostatic potential energy of CO₂ are both higher than that of CH₄ in different gas competitive adsorption systems, indicating that CO₂ is easier to be adsorbed in coal pores.