Abstract: Due to the long-time exposure to radiation, the bundle of fuel element is possible to swell, bend, or deform, causing local blockage, which may cause the local coolant evaporation and threaten the integrity of the fuel cladding. Therefore, it is necessary to study the characteristics of the flow field and resistance in the rod bundle channel under the condition of local blocking. In this paper, particle image velocimetry (PIV) technology was used to visualize and measure the flow fields downstream of the 5×5 rod bundle channel under the local blocking conditions. Flow field data and pressure data of different types of sub-channels (side, corner, interior sub-channels) under the blocking conditions were obtained. The results show that vortices are generated on the walls of the blockage, and increase along the wall to a certain extent and then fall off, and form a backflow zone in the downstream of the blockage. The size and area of the vortices increase with blocking ratio. As the Reynolds number increases, the vortex spreads downstream and does not accumulate near the blockage. It is found that the variation of coefficient of local resistance has a nonlinear increasing trend with the increase of the blocking ratio.