Abstract: The different characteristics of VVER-1000 and Chinese typical two-loop NPPs in the case of LOCA between 10-100 mm under NS/SG mode were researched by using RELAP5 code. The computation result shows that the design differences, especially the safety features and trip signals could significantly influence the operator time windows and effective mitigation measures. The same sequence of Chinese typical two-loop NPPs with adjusted parameters according to the VVER-1000 design concept was calculated, and the results show that the safety margin could notably increase. Thus, this article indicates a practical way to enhance current NPP safety, and would be helpful for developing Chinese 3rd generation NPP and accident manage guidance.