Abstract: In order to solve the adsorbent problem encountered in the purification of methane from coal bed gas by pressure swing adsorption method,the biomass based activated carbon were prepared by the secondary car-bonization- steam physical activation process using coconut shell carbonized material as raw material. The ad-sorption isotherms of CH4 / N2 on coconut shell activated carbon prepared at 298 K and 0-1. 0 MPa were measured by high pressure electronic balance. The pore size structure of activated carbon was measured by specific surface area and pore size adsor- bent instrument. The influence of water vapor activation process parameters to CH4 / N2 adsorption separation perform- ance and pore structure were studied. The CH4 concentration effect of coconut shell activated carbon prepared under the optimum technological parameters was tested by pressure swing adsorption device. The results showed that the equilibrium separation coefficient decreases gradually with the increase of activation temperature,however,the adsorp- tion capacity increases gradually. The best activation temperature is 850 ℃ . The equilibrium separation coefficient and saturated adsorption capacity increase firstly and then decrease with the increase of the vapor flow rate. The best water vapor flow rate is 2. 0 kg / h. With the extension of activation time,the equilibrium separation coefficient decreases after increasing first,methane saturation adsorption capacity increases gradually, and the activation time is also best for 40 min. The activation temperature has significant impact on the development of pore structure. The specific surface area,micropore volume and total pore volume show an increasing trend,indicating that increasing temperature is con- ducive to the development of micropore,and activated carbon with developed micropore can be prepared. The evalua- tion results of pressure swing adsorption show that the volume concentration of CH4 in 20% CH4 -80% N2 simulated coalbed methane increases to 48. 3% with coconut shell activated carbon prepared under the optimum conditions of steam activation process,the enrichment range is more than 25 percentage points,the recovery rate is 80. 58% ,and the productivity is 108. 82 m3 / (t·h). At the same time,the adsorbent also has a good separation effect for medium and high concentration coalbed methane.