This Paper presents sub-cooled boiling two-phase natural convective using computational fluid dynamics(CFD) model for the application to the passive residual heat removal system of boiling water reactor. Sensitivity studies on meshing scheme, grid size, as well as time step are also performed in previous study to minimize the influence of numerical discretization. Comparison between single/ twophase CFD model proved the necessity of two-phase CFD model as it can reasonably predict the temperature jump observed in the experiment which could not be reproduced by single phase CFD model. Discrepancy between numerical simulation and experiment data due to the choice of different turbulent models and CFD software’s simulation results are also discussed in order to verify the best practice for this simulation.. The calculation shows that the the temperature distribution, bubble appearance time and locus predicted by the two-phase CFD simulation for sub-cooled boiling natural convective is well consistent with experiment data, which confirms the numerical calculation creditability and accuracy and the possibility for developing new heat transfer model using such methodology is reasonably suggested.. Base on the built two-phase CFD simulation method, transient characteristics of passive residual heat removal system for ESBWR?Economic Simplified Boiling Water Reactor?is simulated and a promising tank temperature distribution is obtained compared with experiment data, which further strengthen the confidence of engineering application of two-phase CFD model on prediction of natural circulation heat transfer characteristic of passive residual heat removal system.