Abstract: In order to reveal the competitive adsorption characteristics of CH₄ /CO₂ mixed gas in coal, the isothermal adsorption experiments of five different ratios of CH₄ /CO₂ mixed gas in coal were carried out. Experiments show that the relationship between the adsorption amount of pure CH₄ and pure CO₂ and the gas pressure satisfies the Langmuir equation. Under the same conditions, the adsorption capacity of CO₂ by coal is twice that of CH₄; the adsorption capacity of mixed gas of CH₄ /CO₂ with different ratios is always between the single-component CH₄ and CO₂; coal does not adsorb mixed gas independently, but competitively, and CO2 is dominant in the process of competitively adsorption; as the volume fraction of CO₂ in the mixed gas increases, the adsorption selectivity coefficient increases, and it is always greater than 1, indicating that CO₂ injection is feasible to displace CH₄, that is, CO₂-ECBM/CO₂ storage is feasible; the BET multi-component gas adsorption model is more suitable for predicting the amount of CH4 /CO2 mixed gas adsorbed by coal.