In order to achieve the goal of using red mud to remove SO2 from flue gas, red mud and fly ash were used as raw materials, activated carbon as pore-forming agent, and sodium silicate as binder, and the dry desulfurization agent was prepared by extrusion and then calcination, and the desulfurization mechanism was explored. The effects of different pore-forming agent, binder addition and desulfurization temperature on the desulfurization performance of the desulfurizer were studied, the best mass ratio was determined to be m(red mud)∶m(sodium silicate)∶m(fly ash)∶m(activated carbon)=70∶20∶15∶10, and the desulfurization temperature was 250 ℃ to obtain the best desulfurization performance, with a penetration time of 163 min and a penetrating sulfur capacity of 10.484%. The results show that the removal of SO2 by red mud desulfurizer mainly depends on the surface adsorption mechanism and the reaction mechanism between metal oxide and SO2. The surface adsorption mainly depends on the pore size distribution, specific surface area, rich pore structure and surface active centers of desulfurizers. The metal oxides can play adsorption role and chemical reaction with SO2, and the large amount of lattice oxygen and adsorbed oxygen contained in it can catalyze the chemical reaction and improve the efficiency of desulfurization.