Abstract: To study the physicochemical structure characteristics of coal and its effect on the thermodynamic of gas adsorption, the physicochemical structure of coal was characterized by low pressure nitrogen adsorption and FTIR experiment. The gas adsorption curves of lean coal and long-flame coal at different temperatures were measured using isothermal adsorption experiment. Langmuir model and Freundlich model were used to fit the empirical data and the thermodynamic parameter　△G° based on two models was calculated. The results show that Freundlich model is suitable to describe the thermodynamic process of gas adsorption and the gas adsorption process is characterized by spontaneous at different temperatures. It was found that the pore structure of long flame coal is more beneficial to the adsorption process, while the surface chemical structure of lean coal benefits the adsorption process more. The joint action of pore structure and functional groups affects the adsorption capacity of gas. Besides, △G° obviously shows the different characteristics of pore structure of coal. Thus, the adsorption amount and △G° should be considered together for comprehensive evaluation on the adsorption performance of gas with different metamorphic degrees coals.