Abstract: Based on the scale-up model of 2×2 rod bundle channel, an experimental study of effects of mixing vane on lateral flow field in rod bundle channels of fuel assembly was performed with particle image velocimetry（PIV）. The development of lateral flow velocity at different places after the fluid passing through mixing vanes was investigated. The effect of Reynolds number on the lateral flow field was gained by comparing the changes of the flow fields when bending angles equal 20°,25°, 30°, 35°, 40° and 45°. The characteristics of flow fields under four typical Reynolds numbers, which were 33000, 36000, 40000 and 45000, were gained. The results show that both of Reynolds number and bending angle can significantly influence the lateral flow in the rod bundle channel.