Eroded shores are usually the most frequently damaged and severe sections of seawalls. With the increase of extreme weather conditions and the impact of human activities，the problem of coastal erosion has intensified，posing a greater threat to the safety of seawalls and the rear land area. Most of the repairing methods are unable to fundamentally solve the problem of the destruction of eroded seawalls. Based on the case of seawall damage to the north of Zhendong sluice in Binhai County caused by coastal erosion，we analyze the mechanism of coast erosion on the safety of the seawall，discuss the repair measures on the eroded coast，and propose the calculation method of the pile-dam transmission coefficient and the stability of the seawall through field investigation，wave physical model tests，and theoretical calculations. The research reveals that the main reason for the destruction of seawalls on eroded banks is the increase of wave dynamics caused by the increase of water depth，which leads to bottom and surface protection erosion under daily conditions and structural instability under extreme conditions. Based on this，a seawall repair plan for eroded shores with beach protection and reinforcement is proposed，which is verified by the wave physical test to be reasonable and feasible.