The chemical looping combustion (CLC) is an advanced combustion technique that can separate carbon dioxide (CO2) simultaneously. The recyclability and stability of oxygen carriers is very important for the economical efficiency of CLC. The major factor for the deactivation of oxygen carriers is sintering. For most CLC studies, the focus were all on the reactivity of the oxygen carriers, but very few effort was contributed to the sintering properties of the oxygen carriers. This article addressed the characteristic and decay kinetics of surface area for iron oxide in the reduction process of CLC. The results showed that increasing the reaction temperature accelerated the decrease rate of surface area for iron oxide. In addition, with the reduction degree deepening, the grain size of iron oxide increased. Sintering kinetics of surface area decay based on a power law expression model was investigated. The activation energy for surface area decrease of iron oxide in the reduction process was calculated as 89.94 kJ/mol. Sintering and oxygen vacancies creation were the two causes for micro structural variation of iron oxide during the reduction process. Sintering leads to the decrease of surface area for iron oxide, while oxygen vacancies creation results in the porous structure forming.