Abstract: The cooling performance of PRHR HX in main feedwater line break accident was analyzed with LOFTRAN2 code. The analysis results show that the long term cooling is sustaining and PRHR HX is able to cool the RCS to 215.6 ℃ in 36 h even under extreme situation, which conforms to the requirement of advanced light water reactor utility requirements document (URD). The sensitivity analysis results show that the fouling factor of PRHR HX and the initial temperature of in-containment refueling water storage tank (IRWST) may affect the long term cooling performance significantly, so it must be paid attention in plant operation.