Abstract: In order to explore and select the appropriate acid solution to improve the permeability of coal, experiments were carried out to study on the adsorption characteristics of coal samples modified by acid solution at different pH values. Through collecting coking coal samples, eight groups of raw coal and acidification modified coal samples with different pH values were prepared. The industrial analysis and physical parameters test of the samples were carried out, and then the isothermal gas adsorption test was carried out. The experimental results show that: compared to the raw coal sample, acidification modified can reduce the ash content of coal sample without changing volatile coal sample; the true density of the modified sample is similar to that of the raw coal sample, but the apparent density decreases slightly. With the increase of pressure, the gas adsorption capacity of the modified coal sample is obviously greater than that of the raw coal sample. The adsorption constant a decreases with the increase of pH value（except pH=1）, while the adsorption constant b generally decreases with the increase of pH value. The results show that the pore structure of coal body can be changed and the adsorption capacity of coal body can be increased by selecting appropriate pH value solution to modify the specific coal seam, realize the effect of coal seam permeability enhancement finally.