Due to the requirements of safety level of nuclear power plant are gradually improving ,more and more passive systems are used in the advanced type reactor .How‐ever ,the reliability evaluation work for these passive systems is still in the primary stage .In this paper ,based on the reliability evaluation process of passive system ,the physical process of passive system was simulated by RELAP5 thermal‐hydraulics pro‐gram and the reliability of AP1000 external reactor vessel cooling (ERVC) system was evaluated .After the large number of calculations ,the cumulative density distribution curve of the temperature in lower head of the reactor pressure vessel and other parame‐ters were obtained .Combined with specific success criteria ,the reliability of AP1000 ERVC system was got .This reliability evaluation result of ERVC system can be used in the PSA model to better guide the design of nuclear power plants and improve the safety of nuclear power plant .%由于核电厂安全水平要求的逐渐提高，越来越多的非能动系统被用于先进反应堆堆型中，但对这些非能动系统可靠性评价的工作还处于初级阶段。本文根据非能动系统可靠性评价流程，通过RELAP5热工水力学程序模拟非能动系统物理过程，对AP1000反应堆压力容器外部冷却（ERVC）系统进行了可靠性评价。通过计算得到了压力容器下封头温度等参数的累积密度分布曲线，根据不同的成功准则即可获得AP1000 ERVC系统的可靠性。该非能动系统可靠性评价结果可用于核电厂PSA模型中，以更好地指导核电厂设计及提高核电厂的安全性。
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