The invention discloses a smoke desulfurizing agent and a smoke desulfurizing method. The smoke desulfurizing agent comprises 10%-80% of red mud, 5%-50% of aluminum ash, 5%-70% of coal ash and 5%-30% of waste carbon powder according to weight percentage composition. The smoke desulfurizing method comprises the following steps of firstly weighing different raw materials according to composition proportion of the raw materials, uniformly mixing so as to obtain a mixing material, pressing the mixing material into a prism object, and arranging a gas channel in the prism object; arranging the prism object in desulfurizing equipment, connecting the desulfurizing equipment with a smoke pipeline, introducing the smoke generated by the smoke pipeline into the desulfurizing equipment to fully contact with the desulfurizing agent for desulfuration, and discharging when the gas after desulfuration meets the nation discharge standard. The smoke desulfurizing agent and the smoke desulfurizing method provided by the invention have the advantages that respective characters of red mud, coal ash, aluminum ash and waste carbon dust, the red mud, the coal ash, the aluminum ash and the waste carbon dust are mixed into the desulfurizing agent, sulfur dioxide in the smoke is effectively removed, the desulfurization degree can achieve more than 90%, the waste is recycled, the desulfurizing cost is low, sulfur dioxide removal rate is high, and the industrialization is magnified.