Based on the research on the transmission coefficient of pile breakwater in China and abroad,and according to the wave dissipation mechanism of the large diameter cylindrical structure,we determine the main test parameters and test groups,and carry out physical model test.After data processing,we obtain the wave high over the structure,and define that the main factor affecting the transmission coefficient is the relative pitch η,the minor factors are wave steepness H/L and relative ultra Δh/H.On the basis of the Hartmann theoretical formula,and combining the data of the physical model test,we obtain the formula of transmission coefficient.This research provides a scientific basis for the design of large-diameter cylindrical breakwater.