Abstract: The adsorption-desorption behavior of carbon dioxide and methane gases in coal samples were experimentally studied.The replacement experiments of methane by carbon dioxide for simulating the proeess of "CH4 production-C02-injection-CH4 production"were also made in order to enhance the coalbed methane recovery.The C02 and CH4 composition.variation and phase separation curves were obtained.The results show that with the proceeding time of experiments,the competition rate of adsorption for C02 decrease, while that for CH4 increases.However,the reverse results were obtained for competition rate of desorption for these gas phases.It indicates that the adsorption of CO2 is prior to that of CH4. If the amount of injected C02 and／or the C02 concentration is higher,the rate of CH4 desorption and C02 adsorption would be higher.The results of our experiments are significant to commercial production of coalbed methane.