Abstract: In order to verify the effectiveness of the single-phase rod bundle flow in the fuel assembly sub-channel of OpenFOAM, the SST k-ω model was used to simulate the MATIS-H benchmark. The velocity and pressure were solved based on OpenFOAM. The simulation data of OpenFOAM were compared with the data of the MATIS-H benchmark. The results show that the OpenFOAM data are consistent with the MATIS-H benchmark data with a Level 3 mesh. Due to the existence of grid and mixing vanes, the coolant moves closer to the central channel and the distribution of the high and low pressure areas are obvious. A vortex is generated in the sub-channel which enhances the heat transfer on the surface of fuel rod. OpenFOAM has prospects in sub-channel CFD simulation applications.