A three-dimensional dynamic pressure model NHWAVE was used to simulate the wave transmission experiment of a slope breakwater without overtopping,and validated by the experiment data.The effects of wave non-linearity on the wave transmission characteristics of the rubble mound breakwater were investigated using the Ursell number and wave steepness,and relative length(relative breakwater width B/L)was insteaded of absolute length(B)to indicate the width of the breakwater at the calm water surface.On this basis,a new wave permeability coefficient KL was calculated,and the relationship between the wave transmission coefficient and wave non-linearity was discussed.It is suggested that the non-linearity character of waves has a strong influence on the wave transmission coefficient. Finally,based on the results of numerical modeling,an empirical formula of wave transmission coefficient was developed，which provided the reference for breakwater construction and scientific research.