The invention provides an oxidation denitrification device. The device comprises an NaClO2-NaClO solution conveying pump, a desalting water pump, an oxidant preparation bin, an oxidant conveying pump, an oxidation denitrification tower and a lime slurry pump, wherein a first injection gun and a second injection gun are correspondingly arranged at the inner upper part and the inner lower part of the oxidation denitrification tower; a dust discharging valve is arranged at the bottom part of the oxidation denitrification tower; the NaClO2-NaClO conveying pump and the desalting water pump are correspondingly communicated with a first feeding port and a second feeding port of the oxidant preparation bin through pipelines; an outlet of the oxidant preparation bin is communicated with an inlet of the oxidant conveying pump through the pipeline; the outlet of the oxidant conveying pump is connected with the first injection pump; the outlet of the lime slurry pump is connected with the second injection gun through the pipeline. According to the oxidation denitrification device, oxidation and denitrification are coupled into one oxidation denitrification tower, so that the processes are simplified; the operation is easy; the cost is low. The invention also provides a denitrification method of the oxidation denitrification device. The method has the advantages of reducing the operation cost, and being high in denitrification efficiency.