Abstract: The modification of activated carbon used in biogas decarburization and purification through adsorption method was studied,and ammonia used as modifier.The effect of modifier concentration and modification time on the decarburization effect of activated carbon and its surface chemical structure was investigated.The results shown that:1)After the treatment with ammonia water,the activated carbon showed less acid functional groups and more alkaline functional groups.At the same time,the introduction of nitrogencontaining functional groups made the surface hydrophobicity of the modified activated carbon enhanced,the polarity changed,and the adsorption capacity of the gas was enhanced;2)In the concentration range of modifier concentration 5%-25%,the concentration of ammonia water is 10%,the modification time is 12 h,and the modification effect is the best.The specific surface area of activated carbon increases from 413.2 m~2/g to 502.7 m~2/g,21.66%is increased,the micropore volume increased by 39.47%to a maximum of 0.735 cm~3/g,the total pore volume increased by 54.33%to a maximum of 0.963 cm~3/g,and the pore diameter increased by 13.06%to 1.307 nm;3)Simulated biogas（CH₄volume accounts for 60%,CO₂ volume accounts for 40%）adsorption decarburization experiments showed that the best modified activated carbon treatment increased the methane content in the sample gas by 19.96%,and reached 91.53%from 76.30%of the original activated carbon.