In the present study, a two phase transient three-dimensional CFD simulation is carried out to numerically investigate the saturated downward facing pool boiling on a hemispherical heating surface. This simulation is performed within the OpenFOAM framework and a two phase Euler-Euler approach (Volume of Fluid (VOF) model) has been chosen in this research. This code can be used to predict the distribution of the local flow parameters, such as the void fraction, bubble diameter, the velocity of both liquid and gas, the turbulent intensity as well as liquid temperature. Special attention has been devoted to the two phase flow characteristics and vapor morphology along the overheated hemispherical curved surface. For the validation of boiling phenomena, the results of CFD simulation are compared with the visualizations of subscale boundary layer boiling experiment conducted by State Nuclear Power Technology Research & Development Center (SNPTRD) in China. Simulation results show that vapor behavior along the hemispherical curved surface is cyclical, repeatedly forming a stratified vapor layer at the bottom center, which stretches as more vapor is generated, and then flows upwards along from the convex surface. These numerical results show good agreements with the experimental data. Moreover, detailed analysis focusing on the pressure, velocity, void fraction, heating wall temperature as well as the two phase natural circulation flow characteristics are proposed in this paper. It is found that the vapor behavior of downward facing pool boiling on a hemispherical surface is quite different from those on other surface orientations in many respects including the bubble shape, velocity, rise distance and moving trajectory.