In order to reduce nitrogen oxides in the flue gas and improve the quality of the atmosphere, an Mn-CoO-supported pyrolysis coke catalyst was prepared using equivalent-volume impregnation, and then its denitration efficiency was studied in a simulated flue gas denitrification device in the paper. The composition of the flue gas was a mixture of N₂, O₂, NO, and SO₂. Good denitration catalysts were prepared by changing plasma modification time and modified power, MnO load and Mn-CoO load. The denitration mechanism of the catalyst was analyzed by XRD, BET and SEM. The results are: optimal modified power in the plasma system was 60W, and the best modified time in plasma system was 3min; after being modified by plasma, the denitration efficiency of catalysts were significantly higher than conventional calcination catalyst; among catalysts with different CoO loadings (5%, 8%, 10%), 8% CoO loading had the best denitration efficiency, the best denitration efficiency reached 98% and time of higher denitration efficiency had also been extended a lot; Mn-CoO-supported catalysts had a certain SO₂-resistance, and the denitration efficiency of Mn-CoO-supported catalyst > MnO/supported catalyst > un-supported catalyst.