Abstract: In case of severe accident of PWR, large amount of hydrogen may accumulate in the containment. Unsuitable action of containment spray system will change the inert environment of containment, and cause hydrogen challenge or detonation that may challenge the integrity of containment. The condition of the containment pressure for avoiding hydrogen combustion, at different amount of hydrogen, is concluded based on reasonable assumptions and experimental correlations of hydrogen detonation. One conservative spraying mode, upon which spraying pump is manually turned on or off with containment pressure, is proposed in this paper. The analysis results aiming at DAYA Bay Nuclear Power Plant by using MELCOR show that the operation mode is feasible. The impact of pit flooding, spontaneous hydrogen combustion and containment basement compositions on the spraying mode is also analyzed in this paper.