Abstract: In order to quantitatively explore the inundation of the floodplain caused by the river channel blockage, taking the upper reaches of the Bahe River in Shaanxi Province as an example, based on the two-dimensional hydrodynamic model, the water flow movement in the upstream and downstream of the blocked body under different flow rates and different blocking conditions was simulated, and the submerged water depth and submerged range were calculated.The results show that after the vertical blockage, the upstream water depth of the blockage position will increase sharply, and the upstream cross-section velocity will decrease significantly.When the flood peak flow is 127 m3/s, the vertical blockage rate is 100%,the upstream water depth and submerged area are 2.36 and 12.36 times that of the unblocked condition.With the increasing of vertical blockage rate, the water depth difference between upstream and downstream increases, and when the vertical blockage rate of the river reaches more than 50%,the submerged area will increase sharply.When the vertical blockage rate is 75%,the submerged area will increase by 83.43% compared to that when the blockage rate is 50%.When the river is blocked horizontally, the water depth of the upstream section of the blocking body increases slowly.In addition, compared with the benchmark condition of vertical blockage rate 50% + horizontal blockage rate 5%,the water depth and submerged area of the upstream section change more significantly with the change of vertical blockage rate under large flow conditions, while the horizontal blockage is more likely to cause larger submerged area under small flow conditions.The submerged area caused by the river blocking is limited, and the length of the affected river section accounts for about 22% of the total length.The research results can provide theoretical reference for complex flood routing and flood risk reduction in similar rivers.