Abstract: In order to improve coal bed methane production rate, coal samples were modified by acid soak to carry out experimental study in laboratory, then the micro-structure characters of modified coal samples were measured by high-pressure mercury injection method, and the gas adsorption laws of these samples were conducted by the high temperature and high pressure adsorption instrument. The results show that: after soaking in acid solution, the mercury withdrawal efficiency of coal sample is increased and the total pore volume is increased, specific surface area is decreased, the pore volume and specific surface area is decreased; the gas adsorption quantity of acid modified coal samples is reduced, and the modified coal sample reduces the gas adsorption ability.