The invention relates to a treating agent for removing sulfur dioxide, sulfur trioxide and hydrogen sulfide from tail gas of an oil burning boiler. The treating agent is prepared by compounding following components: 2-ethoxy benzaldehyde, 4-methoxy benzyl bromide, cyclohexanone, N,N-diethylethanamine, 3-butene-1-alcohol, 1-tetralone, tricresyl phosphate, N,N-dimethyl trimethylene diamine, 2-methoxy-5-fluorouracil, isopropamide, N-butyloxycarboryl-3-piperidone, ethyl chlorooxoacetate, N,N-dimethyl methylamine, 2-bromine-4'-methylacetophenone, quinoline-2-formaldehyde, absolute ethyl alcohol, and the like. The treating agent is strong in complexing power with target matters, the speed of forming complex and sediment is high, the removal rate can reach 99%, the cost is low, the dosage is less, no scaling is formed and no damage is caused to the environment.