Abstract: Developing the oxygen carriers with large oxygen carrying capacity, high reactivity, and strong cycle stability is one of the research focuses in the chemical looping combustion technology. In this study, the effect of spinel-structured K₃FeO₄ on the reactivity of Fe-based oxygen carrier was investigated based on the density functional theory involving the electronic structural properties such as the density of states, adsorption energy, and activation energy. The results show that when the K₃FeO₄ is loaded on the α-Fe₂O₃(001) surface, the microscopic electronic structure of α-Fe₂O₃(001) surface is changed, the Fe–O bond on the surface is elongated, the O-p orbital electrons transition to a higher energy level, and the electron activity of oxygen atom is improved. The energy barriers of CO reaction with the surface lattice oxygen show a decreasing trend at the three lattice oxygen sites after the loading of K₃FeO₄ which can improve the activity of surface oxygen atoms and make the breakage of Fe–O bond via elongation easier with less energy required. In addition, CO can bond with the more active oxygen atom in K₃FeO₄, and also can combine with the O2 atom to form a new C–O bond, by which CO is adsorbed on the surface in the form of bidentate carbonate that can be decomposed and released as CO₂.