Abstract: The oxidation kinetics of iron sheet in CO₂ -CO mixture was studied by on-line measuring the composition change of the reaction gas using a gas mass spectrometer under different CO₂ partial pressures in the temperature range of 1273 to 1473 K. It is found that the oxidation rate increases linearly with CO₂ paltial pressure, the rate constant decreases with the increase of COJCO volume ratio, and the apparent activation energy of the oxidation of iron sheet is (137.7±15.8)k J·mol^-1. Compared with the results reported, this on-line mass spectrometry analysis can get reliable resuhs, so it can be used to study the gas-solid reaction kinetics.