In this paper, the method of combining Grand Canonical Monte Carlo simulation and Ideal Adsorption Solution Theory was used to study the adsorption performance of CO₂ and CH₄ on NaX zeolite. By comparing the fitting results of simulation data under different adsorption theoretical models and calculating the adsorption heat, a description of the adsorption and separation process of CO₂ and CH₄ gas was obtained. The results show that the adsorption strength of CH₄ molecules is weaker than that of CO₂ molecules, and its adsorption is closer to the ideal adsorption. The adsorption selectivity of CO₂ molecules is decreases with the increase of its content in the air, and decreases with the increase of temperature under low pressure conditions. Therefore, low temperature and low pressure are more conducive to the separation of CO₂ molecules.