Abstract: The cooling enhancement using bypass flow in the ERVC was proposed in this paper. The effect of bypass flow on natural circulation capacity of ERVC for an advanced large size PWR was qualitatively studied by using RELAP5 code. The sensitivity analysis was carried out for some flow parameters and boundary conditions. The simulation results show that bypass flow channel can enhance the convective heat transfer for local region of the ERVC system. With the increase of bypass channel diameters and injecting angle, the convective heat transfer is enhanced. The inlet position has an influence on heat transfer for local region. The results provide reference for the cooling capability and design of the ERVC.