Coating of CaO or MgO on the particle surface can prevent the sticking among iron ore particles effectively during fluidization process. However, CaO and MgO promote the formation of iron whiskers at high temperature, leading to the catastrophic defluidization. The density functional theory (OFF) calculations were implemented to investigate the influence of CaO and MgO on reduction of FeO/Fe2O2 by CO. Our results show that the CO molecule tends to bind to FeO/Fe2O2 on CaO(100) and MgO(100) surfaces through newly formed C-Fe and C-O bonds. The CaO(100) surface will accelerate the reduction reactions which occur on it, in particular, in the initial stage of reactions, however, will slow down the reactions in the posterior stage. For the MgO(100) surface, the reduction reactions which occur on it will be promoted. The positive roles displayed by CaO and MgO in promoting the reduction of FeO by CO accelerate the precipitation of fresh iron and therefore, leading to the formation of iron whiskers. (C) 2016 Elsevier B.V. All rights reserved.