Flue gas circulation is an important method to reduce NOx emission in the iron ore sintering process. In flue gas circulation, NOx is eliminated mainly through the reduction reaction with C or CO, in which CaFe2O4 plays an important role as the catalyst. In this paper, CaFe2O4 was synthesized by the ceramic rout; and the catalytic performance was investigated. The experimental results show that the reduced calcium ferrite (RCF) was superior to unreduced samples in catalytic activity and oxygen tolerance. The results of density functional theory (DFT) calculation and characterization showed that the RCF was in an electron-deficient state, which led to its higher catalytic activity. The electron-deficient state is more conducive to the complexation between the sample and oxygen under an oxygen-containing atmosphere, improving the O-2 tolerance in the CO-NO reaction. The results suggest that decreasing the O-2 content in the circulating flue gas will enhance the reducing atmosphere in the sintering bed and facilitate the catalytic reaction between CO and NO, which is beneficial for NOx removal.