Abstract: The pressurizer optimization scheme built by considering engineering constraints was modified. Based on Qinshan Ⅰ Nuclear Power Plant primary loop in which the original pressurizer design scheme was replaced by the modified one, a RELAP5 model was built and the performants of optimized pressurizer during SBLOCA-LOFW and LOFW-ATWS accidents were studied, and the results were compared with that of the original model. The results show that modified optimization scheme has yielded pressure increase in the secondary side of steam generator, which is in favor of ensuring steam turbine efficiency and safety. In the scope of this study, the capability of the optimization model coping with accidents is comparable with that of the original one.