Circular ramp overtopping wave energy converter (CROWN) is an offshore overtopping wave energy converter that consists of a reservoir surrounded by a circular ramp and an outflow duct installed with a low water head turbine. Physical model experiments were conducted in a wave tank as a preliminary study at Ocean University of China. The wave overtopping behaviors demonstrated that guide vanes can effectively lead the wave water motion on the ramp for overtopping into the reservoir. An analysis of the overtopping discharge shows that the resonant zone is located in the smaller relative wave length domain. Within the scope of shape parameters used in this study, guide vanes and milder ramp slopes were found to significantly enhance the overtopping discharge. The orientation of the guide vane angle also had a large influence on the overtopping flow rates for smaller relative wave heights and lengths. The experimental results are presented with the aim of designing and optimizing the shape parameters of CROWN for a future prototype device.