Abstract: The adsorption mechanism of inert gases CH₄，N₂ and CO₂ on coal surface was analyzed by using density functional theory (DFT) M062X method. According to the Millikan charge distribution of each atom in the  coal molecules,  adsorption vacancies on the surface of coal molecules were determined. The adsorption models of CH₄，N₂ and CO₂ as single component gases  on the coal surface were established on each adsorption vacancy. By analyzing and comparing the microscopic parameters such as bond length,  bond angle,  adsorption distance and adsorption energy of each adsorption model,  the author obtains that  the affinity order of the three kinds of gas adsored on coal surface is  CO₂>CH₄>N₂, and reveals  the microscopic states of CH₄，N₂ and CO₂ adsorption on coal surface.

Key words: adsorption mechanism,  , density functional theory,  , adsorption vacancy,  , Millikan charge distribution,  , microscopic state