Taking the Shengsi sea in north of Zhejiang as the research area，the distributions of the wave field inside and outside the protected areas of Zhoushan Sijiao converter station are simulated by the combined application of SWAN model with nested grids and BW model，while the results of the wave factors in front of the cofferdam gap by SWAN model are taken as the boundary conditions of BW model.The results show that the wave directions turn to SSE when the E，ESE，SE direction waves propagate from the outside sea areas to the front of the Maguan dike，and the maximum wave height of the front of the cofferdam gap is from the ESE direction.The diffraction waves attenuate obviously when the waves enter the protected areas，and the design wave factors with 100-year return period and 50-year return period are obtained by the superposition of the diffraction waves and the local wind waves，i.e.the significant wave heights of 1.08 m and 0.98 m.The phenomena of wave refraction，diffraction，and reflection within the large range of the bathymetry inside and outside the protected areas is simulated with high precision，so the combined application of SWAN model and BW model in Zhoushan Sijiao converter station achieves good efficiency on the design wave calculation，thus it will provide reference for design wave calculations of similarprojects.