In coastal protection breakwater engineering,vertical wall is constructed by hydraulic sliding panel technology,and rubble slope is formed underwater in front of the wall.This kind of composite breakwater has shown good safety and stability in engineering practice.Three types of breakwaters (vertical breakwater,rubble-mound breakwater and composite breakwater) are tested under different wave conditions,and the mechanism for the better stability of the composite breakwater comparing with other 2 type breakwaters is studied.The test result shows that the rubble slope reduces the wave pressure on the vertical wall and wave impact significantly;the vertical wall also prevents the rubble mound from moving behind the breakwater and avoids excessive damage of the rubble slope.The combination of them produces better stability comparing with the vertical dike or the rubble slope.