Abstract: Based on computational fluid dynamics（CFD） method, eddy dissipation concept（EDC） model coupled with the P1 radiation model is used to simulate the ThAI-HD12hydrogen combustion experiment carried out in Germany, which is in good agreement with the experiment. In addition, by modifying the reaction mechanism, the results match better. By changing the ignition position and hydrogen concentration, the changes of pressure and temperature in the containment are calculated. The results show that buoyancy has a significant impact on the propagation of hydrogen combustion flame in the containment;the higher the hydrogen concentration is, the faster the ignition is, and the faster the combustion rate is. But when the concentration increases to a certain extent, the ignition is no longer advanced. The hydrogen combustion flame in the containment is affected by many factors, and finally presents a “tulip shaped flame”.