Abstract: As the most important structure to enhance fuel assembly and thermal hydraulic performance, spacer grids are of great importance to improve the economic efficiency and the safety of nuclear reactors. The numerical simulation and experimental study of the mixing vane grids design have drawn much attention in the past years. Key components, such as mixing vane and dimple, in spacer grids have a large impact on the mechanical and thermal hydraulic performance. In this paper, the simulation pressure drop value was compared to the experimental data to provide initial validation of the CFD method. Then the effects of mixing vane angle and dimple shape on the flow field downstream of spacer grids were analyzed based on the validated CFD model, meanwhile the code-to-code comparison between CFX and STAR-CD simulation results was also made to give an initial evaluation of CFD calculation.