Abstract: Multi-pendulum wave power converter is a device for better ability to capture wave energy by taking advantage of its multi-pendulums. Hydrodynamic performances of a multi-pendulum system and a single pendulum system are examined in this study, using numerical simulation on the three-dimensional potential theory and considering different gap sizes of pendulum. The results show that in a multi-pendulum system, the interaction of its multi-pendulum produces resonances of peak values different from those in a single pendulum system, and that as the gap size increases, its influence on hydrodynamic performance takes a trend of first increasing then decreasing.