Abstract: In order to study the effect of surface acid modification on gas adsorption characteristics of coal,the coal sample was modified by soaking with acid.The gas adsorption law of modified coal samples was studied by isothermal adsorption instrument,and the pore structure characteristics of each coal sample were tested by high pressure mercury injection instrument.The research results show that acid modification has a great influence on the coal pore structure,and the acidification can connectinternal pores of coal,after soaking by acid,the number of adsorption pores of coal sample decrease and the number of medium and large pores of coal sample increase.With the increase of soaking time of acid solution,the gas adsorption capacity of coal presents a nonlinear change of first fast and then slow;under the action of acid liquid,the adsorption capacity of coal gas declines and the adsorption rate reduces.