Abstract: Uncontrolled withdrawal of rod cluster control assembly bank from a subcritical or low power startup condition is classified as a RCC-P condition Ⅱ event and always one of the most limiting events in the safety analysis for the nuclear power plant. Based on typical three-loop PWR, the effects of different initial arrangements of the shutdown banks at the hot-shutdown state on the DNBR margin were studied. The results show that the DNBR margin is further increased by optimizing the initial arrangements of the shutdown banks at the hot-shutdown state in order to assure the enough shutdown margins.