For a pile cap structure,the theoretical method and numerical simulation method are used to calculate the wave force under the action of waves,and the physical model test is carried out to verify the comparison.For theoretical methods,Morison formula is used to calculate the wave force of piles group,and the diffraction theory is used to calculate the wave force of cap；the numerical model is based on Fluent to solve navier-stokes equation,and the source term is modified by UDF to realize wave making,and the numerical water tank is established.The results show that the force of the structure calculated by the theoretical method is slightly smaller than that of the test result because the interaction between the upper and lower structures is not considered；however the numerical model obtained good results when calculating the pile,cap and the overall force,especially when there is wave on the cap,it can also get good results.It is commended that the numerical method should be used to calculate the wave force of pile cap structure.