The invention provides a denitration catalyst as well as a preparation method and application thereof. The denitration catalyst comprises CeO2 doped with a Mn compound, wherein a molar ratio of Ce atoms to Mn atoms is (0.2-5):1, an average particle diameter of the denitration catalyst is 1 to 100 nm; a surface of the denitration catalyst has active ions, and the active ions include inorganic acidions. The denitration catalyst provided by the invention has excellent denitration efficiency, is inexpensive and environmentally friendly, and has no obvious toxicity; and in addition, the denitration catalyst can remove chlorine-containing volatile organic compounds while removing nitrogen oxides, has excellent chlorine poisoning resistance, and is suitable for synergistic removal of the nitrogen oxides and the chlorine-containing volatile organic compounds in flue gas in industries such as metallurgy, steel sintering and waste incineration.