This study presents a detailed kinetic mechanism conducted by CHEMKIN for the homogeneous decomposition of SO3-H2O vapor in the sulfur-iodine cycle. The kinetic mechanism involving 27 reactions and 11 species was validated by experimental results. The effects of temperature, SO3/H2O ratio, residence time, and pressure on the decomposition rate of SO3 were studied by modeling. SO3 conversion rapidly increased with increasing temperature but only moderately increased with the addition of H2O in the kinetic process. The SO3 conversion ratio was slightly promoted with residence time at 1000 K and 1100 K. Meanwhile, SO3 conversion sharply increased with reaction time at 1300 K to 1400 K. The results of sensitivity analysis showed that elementary reactions (2) SO3 = SO2 + 0, (3) SO3 + 0 = SO2 + O-2, (12) 2HO(2) = H2O2 + O-2, and (13) HO2 = H + O-2 had important functions in SO3 decomposition. The reaction path of homogenous H2SO4 splitting was constructed based on detailed kinetic modeling and sensitivity analysis. (C) 2014 Elsevier Ltd. All rights reserved.