Abstract: Extreme sea conditions such as typhoon waves and submarine strong earthquakes will induce island and reef bank slope instability, resulting in chain disasters such as blow-fill collapse and upper infrastructure damage, so it is very important to analyze the seepage and dynamic stability of island and reef slope. Taking the typical revetment slope engineering of the South China Sea dredger reef as the research object, firstly, the finite element method is used to solve the internal seepage field of the island reef slope with or without revetment under the typhoon sea condition, and then the extreme seismic dynamic load is considered. Then, the dynamic model of stress field and pore pressure field of the island reef slope under the action of seepage and dynamics was developed. Finally, based on the limit equilibrium method, the overall and local stability of the island reef slope with or without revetment is discussed under the condition of seepage and dynamic load. Through the horizontal and vertical comparison of a large number of numerical calculation results under extreme sea conditions, it is found that the breakwater improves the overall stability of the island and reef bank slope and ensures the long-term safety of the blow-fill body, and the research results can provide reference for the construction of similar projects.