Aiming at the problem of the strong impact effect of overtopping on the armour blocks of the breakwater's rear slope under long-period and rough waves，taking a Mediterranean petroleum and natural gas terminal expansion project as an example，we propose an optimized scheme of a cantilevered protective structure by widening the rear edge of the crown wall's bottom slab，carry out three-dimensional physical model tests and study of water conservancy industry standards，and analyze the stability results of this scheme.The results show that the cantilevered part，by widening the bottom slab of the crown wall，can shield the top of the rear slope armour blocks from the direct impact of overtopping.The armour blocks beyond the cantilevered part are located below the water surface.When the water depth is thick enough，it can reduce most of the energy of overtopping，thus satisfying the stability requirements of the armour blocks.Compared to increasing the elevation of the crown wall or enlarging the armour blocks of the rear slope，the cantilevered protection scheme has a low cost and good protective effect.