Abstract: In dealing with the hydrogen risk management under severe accident, the study of the minimum inerting concentration (MIC) on hydrogen of different gases was carried out. And the mechanism difference between conventional inert gas and freon was elaborated. The inhibition factor of inert gas was calculated by the group contribution method. The MIC was predicted with flame propagation speed and stoichiometric concentration. The results show that the MICs of HFC-134a, HFC-245fa and HFC-125 are 15.87%, 14.12% and 10.39%, respectively. HFC-125 shows the best inerting performance. The minimum inhibition concentrations of the three freon are 34.9%, 32.7% and 25.9%, which are much lower than N₂ and CO₂ with 94.5% and 90.9%.