Abstract: This paper presents an experimental study on hydrodynamic performance of a bottom-hinged flap wave energy converter in different conditions and different swing flap mass distributions. The device is composed of a magnetic power extracting system that is controlled with magnetizing current and a torque sensor. The swing flap is a hollow structure vertically divided into five separate chambers, and its mass distribution can be controlled by filling water into different chambers. The design of experiment was verified by comparing experimental and numerical results; the effects of wave condition and flap mass distribution on the captured power-width ratio of the converter and the dynamic pressure on the swing flap surfaces were analyzed. The results indicate that with the increasing wave amplitude, the captured power-width ratio decreases and the flap dynamic pressure increases. And a larger captured power-width ratio and lower dynamic pressure will occur when either the two bottom flap chambers are filled up with water in the case of short waves or only the bottom one is filled up in the case of long waves.