Many cases of dam/levee failures have shown that wave overtopping is one of the most important reasons to cause dam/levee break. The collapse of dam/levee caused by wave overtopping is mainly due to the erosion behind the dam/levee. This is because the flow combining with eddies and vortices generated by wave overtopping scour the ground behind the dam, which causes the instability and collapse of the dam. By considering several important factors, such as the downstream slopes of dam, soil properties, and wave characteristics, we carried out an experiment to study the soil erosion behind the dam due to wave overtopping. The change of topography behind the dam, depth of scouring, and the amount of soil loss are measured quantitatively. We also applied efficient methods to digitize the experimental measurements and visualize the experimental results. The experimental data is then analyzed in details and the practical way to protect the erosion behind the levee is also discussed. This study provides useful methods for the dam/levee protection in Zhejiang Province, and also has important contributions to research related to soil erosion and dam break due to wave overtopping.