In order to determine the defensive capability of the downtown section of flood wall in Shanghai along the Huangpu River, using monitoring data of flood wall elevation from 2012 and design parameters of the flood wall along the Huangpu River, the Monte Carlo method was applied to calculate the overtopping probability of the flood wall with different tide levels under the current conditions and future conditions of sea level rise, propose evaluation criteria for overtopping risk analysis of the flood wall, and quantify the corresponding overtopping risk. The results show that the current defensive capability of the flood wall is clearly insufficient and Huangpu River flood prevention is inadequate considering the rising water level of the Huangpu River in recent years and the continuing sea level rise that will occur in the future. The high-risk area of overtopping is concentrated upstream of the downtown section of the flood wall. The overtopping risk of the flood wall is related not only to the lack of elevation but also to different designed tide levels adopted in different sections.