For the calculation of wave force on the vertical structure with low pile cap,the design usually refers to the calculation method of wave force on the vertical wall building in the Code of Hydrology for Harbour and Waterways. However,because the front line of pile caps is not in the same line with the vertical wall below the pile caps,the wave forces of the two structures are different.Taking the Third Runway Extension Project of Shenzhen Airport as the research object,we study the wave force variation law of vertical dike with low pile cap under irregular wave action by physical model test.The results show that the impact pressure at the bottom of the cap reaches its peak value near Δh/Hs=0.2;the wave pressure at the front of the cap is less affected by the structure of the cap,and its variation law is similar to that of the vertical wall building;when the wave pressure of the vertical wall under the cap is -0.5＜ Δh/Hs=1.5,the impact pressure has obvious characteristics,which is several times that of the wave pressure of the ordinary vertical wall building.