Abstract: The simulation of AP1000 passive containment cooling system based on SimCont was studied. The transient response of passive containment cooling system and the functional performances of the main equipments were simulated and the simulation tool was comprehensively assessed aiming at the main steam line break accident and the double-ended break of cold leg of coolant loop accident which were the most severe design basis accidents. The code’s performance was estimated. The results show that the model of SimCont can well reflect the function of passive containment cooling system, and the calculation results are consistent with that in the safety analysis report.