Gaseous elemental mercury removal by activated carbon impregnated with SO2 was studied under simulated flue gas conditions. Brunauer-Emmett-Teller (BET) measurements and X-ray photoelectron spectroscopy (XPS) were used to compare the physicochemical characteristics of original activated carbon with the modified samples. It was found that the activated carbon was impacted by the modified temperature, leading to a decline in specific surface area; however, the pore structure with the carbonyl groups improved mercury removal by 46.16%. In addition, the easter group increased by 59.85% in the oxygen-containing functional group. The formation of sulfur-containing functional group was beneficial to the improvement of mercury removal ability. The effects of different sulfur-containing compounds on the performance of mercury removal were further studied. The results revealed that the mercury removal performance of activated carbon featured with sodium sulfide, elemental sulfur, and sodium thiosulfite is better than that of sodium sulfite and sodium sulfate. The inactivated sample was impregnated with SO2 for sulfur-loading thermal regeneration, and its mercury removal performance was compared before and after regeneration. The average efficiencies for mercury removal of the three regeneration cycles were 89.71%, 85.48%, and 79.92%, respectively. The results show that it is feasible to regenerate the deactivated activated carbon by sulfur-loading thermal regeneration, providing a guidance for industrial application prospect.