Based on the fixed bed model test, we compare the changes of hydrodynamic factors of Oujiang estuary including the water level, flow, flow, branch channel’s diversion ratio before and after construction of Wenzhou-Qidu bridge, analyze and forecast the variation of flow pattern and near the bridge and the influence on flood control and navigation. The result shows that the construction of the bridge has no significant effect on flood control and drainage of Oujiang and will not change the nature of the seven North-South branch channels, and has little affect on the port channel.