Abstract: The emergency cooling water is injected into the reactor core by gravity in the large advanced passive PWR nuclear power plant during the long term core cooling (LTCC) following loss of coolant accident (LOCA). The resistances of swing check valves in the safety injection lines vary with flow rate causing unexpected increase in the resistance of safety injection lines. A model according to the swing check valve resistance performance was implemented into the best-estimate LOCA analysis system code in this study. The cases of LTCC following a guillotine double-ended direct vessel injection (DEDVI) line break were analyzed using the improved code. Compared with the previous calculations, it’s found that the swing check valve resistance performance has a little effect on LTCC following a LOCA in the large advanced passive PWR nuclear power plant but is important to the ability of safety injection in some situations with inadequate safety margin.