Abstract: Based on the 31 years wave observation data at Chongwu hydrological station from 1976 to 2007, Pearson Ⅲ type of frequency curve fitting analysis is used to calculate the characteristic wave parameters in conditions of different return period in Chongwu. Besides, the CGWAVE model, an inshore wave numerical model based on the elliptic mildslope equation, is used to simulate the Xisha Bay return period wave field for the design wave parameters. The simulation result shows that the seafloor topography of Xisha Bay strongly influences coastal wave, causing the uneven distribution of wave height and wave direction. Islands and reefs are natural barriers. The eastern waters is protected by Guiyu island and Mintai pier. Wave reflection and diffraction obviously play an effective protection on the sheltered dock. Moreover, different reflection coefficients of different geological boundaries will significantly lead to the variations of nearshore wave height distribution.