Abstract: The wave overflow is a phenomenon that the water level caused by strong storm surge in front of the seawall exceeds the top of the seawall and the seawall is subjected to the combined action of the overtopping and overflow. It happens when the sea water level (SWL) is higher than the level crest under the impacts of the strong storm surge. With the presence of the combined wave and surge overtopping, it is very easy to cause large-scale erosion of the inner slope of the seawall and even break the seawall, resulting in catastrophic consequences. Based on the experimental results of the full-scale flume tests, the hydraulic characteristics of the flow along the landside slope of the seawall during combined wave and surge overtopping are tested and analyzed under different slope protection conditions, including roller compaction concrete, articulated concrete block and high-performance turf reinforcement mat. The empirical equations for average water depth and overflow velocities on the landside slope during the combined wave and surge overtopping are proposed under different slope protection conditions. It is found from the analysis results that the distribution of the wave height along the landside slope can be represented by the Rayleigh distribution, and the relationships between the characteristic wave heights and the characteristic peak water depths along the landside slope are established during the combined wave and surge overtopping. At the same time, the empirical equations for the root-mean-square wave height and wave velocities along the landside slope of the seawall during the combined wave and surge overtopping are also proposed in this paper. The research results can provide references for related researches on the landside slope protection under the combined wave and surge overtopping conditions.