The invention provides a flue gas denitration reaction catalyzing device, and aims to overcome shortcomings in the prior art. A cyclone separator for separating a solid denitration catalyst from flue gas is placed inside a fluidized bed reactor, powerful vortex is generated by the cyclone separator, by advantages of the 'boiling' state of a circulating fluidized bed, the purpose of flue gas denitration is achieved, loss of the catalyst is reduced, and meanwhile, time for contact between the flue gas and the solid denitration catalyst is prolonged, so that the flue gas and the solid denitration catalyst can be mixed fully. The flue gas denitration reaction catalyzing device has the advantages of low construction and maintenance cost, speediness in use, good denitration reaction, high denitration rate and the like.