Dayaowan port area is the main area of Dalian container port,of which the comb-type caisson structure was adopted for the north breakwater.Affected by typhoon,barrier boards inside the cavity were tilted and pushed,and the rubble filled bed was scoured.In order to acquire the causes of bed scour,we carry out a model test with the nonlinear wave flume.The analysis indicates that severe wave turbulence inside the cavity leads to significant buoyancy stress in bed,which is the the main cause of barrier board instability and bed scour.The wing plate trepanning scheme can effectively reduce the buoyancy stress in the bed,while there will be increased wave and velocity to some extent.Considering comprehensively the factors such as bed stability,wave penetration and construction conditions,we determine to open a 3 meters hole in the wing plate and increase the thickness of barrier boards from 0.5 m to 1.0 m.The model test demonstrates the feasibility of the plan.