The structure of water flow around the submerged dike with variable slope is complex and changeable. Based on the Hechangzhou submersible dike project，this paper analyzes the reasons of topographic scour and soft bank damage for the submersible dike. Based on data collection and model analysis，this paper summarizes the correlation between the elevation of the dike top and water level and flood season at the scour site，and analyzes the hydrodynamic characteristics. The following influential factors are obtained：strong combined flow over the dike and around the dike，large flow and rapid retreat of the Yangtze River，and poor stability of the riverbed of the binary soil layer structure. The scour development can be restrained by using the sandbag and stone.