Abstract: With an integral system analysis computer code, the assumed hydrogen control system was analyzed and optimized for 600 MW nuclear power plant. Basic principles for optimization of the hydrogen control system and a set of guidelines which can be implemented in projects were put forward. During the severe accident induced by large-break loss-of-coolant accident (LB-LOCA), the assumed hydrogen control system ensures that the average and local hydrogen concentrations in compartments are less than 10%, matching the hydrogen control and risk analysis standard of United States Nuclear Regulatory Commission (USNRC) 10CFR. Changing the layout of the autoca-talytic recombiners and with the hydrogen risk effectively mitigated, the evaluation of the optimization indicates that the optimization mode 2 is better than the optimization mode 1, and the optimization mode 1 is better than the former one.