Abstract: In order to solve the problem of adsorbents for the separation of CH_4/CO_2 from coal bed methane,activated carbon adsorbent was prepared by steam activation process with coconut shell carbonized material as raw material. The effects of activation temperature,activation time and dosage of modifier on the separation performance of CH_4/CO_2 by pressure swing adsorption were studied. The results show that the optimum conditions for preparation of activated carbon adsorbent are as follows: carbonization temperature is 600 ℃,activation temperature is 800 ℃,activation time is 30 min,dosage of modifier is 10%. Under the optimum conditions,the saturated adsorption capacity of the prepared activated carbon adsorbent for CH_4 and CO_2 is 2.34 mmol/g and 3.23 mmol/g respectively. The equilibrium adsorption separation coefficient is 10.27,which is 190% higher than that without modification. There is a good separation effect for CO_2/CH_4. The CO_2/CH_4 equilibrium adsorption separation coefficient and the adsorption capacity of CO_2 and CH_4 increase firstly and then decrease with the increase of activation temperature. This is because when the activation temperature reaches 800 ℃,the activation temperature reaction speed increases significantly,which makes the wall of the micropores easy to burn through to form mesopores,and even further form macropores. The specific surface area of activated carbon adsorbent decreases,the number of micropores decreases,and the adsorption capacity decreases. The CO_2/CH_4 equilibrium separation coefficient and the adsorption capacity of CO_2 and CH_4 increase at first and then decrease with the extension of activation time. The reason is that after the activation time reaches 30 minutes,more water vapor reacts with the carbon to burn through the micropores,resulting in the decrease of the specific surface area and volume of the micropores,as well as the decrease of the adsorption capacity of adsorbent for CO_2 and CH_4,and the reduction of CO_2 adsorption capacity is more obvious. The equilibrium separation coefficient of CO_2/CH_4 increases gradually with the increase of modifier content,and the adsorption capacity of CO_2 and CH_4 increase firstly and then decrease,The adsorption performance of the adsorbent for CO_2 is significantly improved,while the adsorption performance for CH_4 is significantly reduced.