Taking the seawalls of power facilities in the high shoal and steep slope topography of an island in Zhoushan, Zhejiang as an example, 3 factors that influence the seawall overtopping rate, including the berm width, the berm superelevation and the height of the parapet wall were studied respectively by physical model experiment and sensitivity analysis was carried out by the method of variance analysis. The results show that the most significant influencing factor of the wave overtopping is the berm superelevation, then the height of the parapet wall and the berm width is the least. The dimensionless wave overtopping rate exhibits obvious exponential relationship of decrease with an increase for the top of the parapet wall superelevation. A reasonable layout method of the seawall structures for power facilities is proposed based on the above analysis.