Abstract: In order to study the optimal equation and fast calculation model of CO₂ compression factor suitable for coal adsorption among 6 kinds of gas state equations commonly used in engineering, such as Virial, V-d-W, R-K, S-R-K, P-R and Tongjingshan, three coal samples with different metamorphism degrees were taken as research objects. The CO₂ adsorption capacity, CO₂ adsorption constant and adsorption isotherm of coal obtained by using the above six equations at the test temperature of 30 ℃ were measured by volumetric method. The research shows that: compared with the CO₂ compression factor provided by the National Institute of Standards and Technology (NIST), the maximum absolute error of CO₂ compression factor obtained by Viral state equation is 0.38%. The adsorption isotherm has the highest goodness of fit; the absolute value error of the measured CO₂ adsorption constant a is the smallest, and the optimal gas state equation to determine the adsorption CO₂ compression factor of coal is the Viral equation. At the same time, a simple and fast calculation model of CO₂ compression factor is proposed when the test temperature is 30 ℃. After testing, the absolute error of the absolute value of the CO₂ adsorption constant a calculated by the US standard is less than 1%, and the operation is simple, fast and accurate.