Abstract: Based on computational fluid dynamics (CFD) method, two-phase simulation and application research of subcooled boiling natural convection was carried out. Natural convection experiment of the side wall heating cylindrical tank subcooled boiling was simulated by two-phase CFD transient simulation, and the time for simulation was 1 500 s. By model setting and simulation method research, the result repeated the temperature jump reasonably when subcooled boiling occurred in experiment. The consistent temperature distribution, bubble appeared time and appeared position with those of experiment were got, which confirmed the numerical calculation creditability and accuracy. Then, two-phase CFD simulation was used in ISP-42 experiment based on ESBWR (Economic Simplified Boiling Water Reactor) passive residual heat removal system, and the same temperature distribution with that of experiment was got. The research results show that using two-phase CFD simulation on passive containment cooling system and passive residual heat removal system application research is reasonable, and it can be used to calculate heat transfer coefficient and develop new heat transfer model in the future. This research makes significant value in industry application search on two-phase natural circulation heat transfer characteristic of passive containment cooling system and passive residual heat removal system.