Abstract: In order to research the effect of metamorphic grade of coal on gas adsorption, on the basis of the existing research results, isothermal adsorption test was carried out with dry coal samples of long flame coal, gas coal and anthracite coal, through pore structure and connectivity obtained by mercury injection experiment, control effect of pore development characteristics on gas adsorption capacity was studied, in addition, other factors such as macromolecular structure, equilibrium moisture content and maceral group were considered. The results show that characteristic of pore development, macromolecular structure, equilibrium moisture content and maceral group have comprehensive effect on gas adsorption capacity, and characteristic of pore development is the main factor, as for coal with different rank, pore structure characteristic and adsorption capacity show a positive relationship, moreover, coal macromolecular structure affects adsorption capacity through changing effective specific surface area, adsorption between coal molecular structure and methane molecules and moisture content, equilibrium moisture content and maceral group affect adsorption capacity through changing specific surface area.