When an accident of a nuclear power plant happens, hydrogen can be generated by the chemical reaction between Zircaloy coating surrounding a nuclear fuel rod and water outside it due to the increase of the temperate around a nuclear fuel rod. In the containment, the existence of hydrogen could lead explosion affecting the integrity of the reactor. Therefore, it is essential to accurately predict the hydrogen behavior in the containment. In this study, using the Fluent, we investigate the hydrogen behavior in the containment called PANDA. Particular attention is paid to the characteristics of a stratified layer made in the containment. To do so, the influence of the stratification factors such as velocity, temperature, various location of break and so on is examined. From these data we would recognize the flammable and detonation regions, and have some idea about the mitigation of the accident due to the hydrogen.