Abstract: In order to study the impact of pressure on gas adsorption law in coal seam, a dynamic gas adsorption experiment system under constant temperature and pressure was designed and installed, the adsorption characteristics of four kinds of coal samples were studied under four initial different gas pressure. By processing the test data, the measured change curves of cumulative gas adsorption amount over time and the change curves of the adsorption rate over time were obtained, the mathematic model of gas adsorption was established and it had a high fitting degree with the measured change curves. The results showed that there was a positive correlation between limit gas adsorption amount and pressure, while the greater the initial pressure of gas adsorption was, the faster the adsorption rate was.