Currently, most advanced oxidation denitrification technologies require long flue gas residence time to obtain ideal NO removal efficiency. The NaOH-catalyzed H₂O₂ system proposed in this paper can obtain 98% NO removal efficiency under the condition of flue gas residence time of 3 s. The mechanism of NO removal and H₂O₂ decomposition to O₂ were proposed. It was confirmed with ESR (Electron-spin-resonance), inhibitor experiments and UV-Vis spectrophotometer that the main group in the reaction process was·O₂^- radicals, which reacted with NO to form ONOO^-, and ONOO^- would be gradually transformed into NO₃^- and NO₂^- in the air. The effect of some primary factors on the NO removal efficiency and the percentage of H₂O₂ decomposition to O₂ were also investigated. The increase of initial pH has a positive effect on NO removal, while the promotion of NO removal by increasing H₂O₂ concentration and reaction temperature is limited and the increase of NO has a negative effect on NO removal. Initial pH has a dual impact on the percentage of H₂O₂ decomposition to O₂, H₂O₂ concentration and reaction temperature promote the decomposition of H₂O₂ to O₂, while NO concentration has an inhibiting effect on it.