The invention relates to the technical field of papermaking flue gas denitration and in particular relates to a denitration system. The denitration system comprises a DCS controller, a urea dissolving tank, a urea solution storage tank, a urea high-pressure pump, a urea regulation valve, a mixer, a spray gun, a return feeder and a chimney, wherein the urea dissolving tank, the urea solution storage tank, the urea high-pressure pump, the urea regulation valve, the mixer, a spray gun, the return feeder and the chimney are sequentially connected with one another; the DCS controller is respectively connected with the urea dissolving tank, the urea solution storage tank, the urea high-pressure pump and the urea regulation valve in a controlling mode; the chimney is internally provided with an oxynitride concentration detection circuit, the oxynitride concentration detection circuit is used for acquiring a concentration signal of oxynitride in flue gas of the chimney in real time and sending the concentration signal of the oxynitride in the flue gas of the chimney to the DCS controller, and the DCS controller is used for controlling the chimney to discharge the flue gas according to the concentration signal of the oxynitride in the flue gas of the chimney. The denitration system has the advantages of ideal denitration effect, high denitration efficiency, small loss in flue gas discharge of a boiler, and low production cost.