The catalytic reduction behaviours between NO and CO on a CaFe₂O₄ surface were studied using flue gas recirculation. The reaction mechanism and control principle were investigated via experiment and theoretical calculations. The experiment results show that CaFe₂O₄ can catalyse the reduction of NO by CO, and the NO conversion rate increases with the increase in CO concentration. The theoretical calculations indicate that the CO–NO reaction on CaFe₂O₄ surfaces complies with the Eley–Rideal mechanism, and the reaction path is controlled by nitrogen, oxygen and isocyanate radicals. Specifically, the dissociation of NO into nitrogen and oxygen radicals, and the formation of subsequent isocyanate radicals dominate the reaction. The results provide new insight into the intrinsic reaction mechanism and the meso-scale control principle, allowing us to propose a novel process design scheme to improve the NO_x emission reduction efficiency in the flue gas recirculation process.