To enhance the SO2 adsorption of biochar, CO2 activation and impregnation with methyldiethanolamine (MDEA) was simultaneously employed to improve its physicochemical characteristics. Furthermore, the effects of the pore structure and nitrogen functionality on SO2 adsorption were also explored. The results show that after CO2 activation, the specific surface area of biochar increased from 56.91m(2)/g to 755.35m(2)/g, while this figure dropped to 25.54m(2)/g or even lower after impregnation with MDEA. Although the pore structure of activated biochar was destroyed, the surface nitrogen content of the nitrogen-enriched biochar (with 10% MDEA impregnation) increased from 1.46% to its highest level (7.20%); moreover, as indicated by Fourier Transform Infrared (FTIR) spectroscopy, the nitrogen functional groups introduced on the surface of the nitrogen-enriched biochar were mainly C-N. After 10% MDEA impregnation, the maximum SO2 adsorption capacity increased from 57.8 mg/g to 156.2 mg/g. Changes to physical and chemical properties in the nitrogen-enriched biochar indicate that the nitrogen functional groups on the surface are more important than the pore structure for SO2 adsorption at 393 K, and that the dominant nitrogen species are quaternary nitrogen.