The effects of structure geometry of multi-stage overtopping wave energy converter (OWEC) are studied using two-dimensional numerical simulation. Two design strategies, adaptive slot and overlap ramp, are investigated. The hydraulic efficiency is used to determine the overtopping performance. The numerical results show that the non-adaptive layout in combination with average slot width of 0.4 m gives optimal performance in the range of considered parametric space. The larger slot gives the smaller reflection rate, while transmission rate is slightly affected and can be neglected. The second design strategy, overlap ramp, is applied to both non-adaptive and adaptive multi-stage devices. The overlap ramp layout slightly affects the overall hydraulic efficiency of OWEC device. On the other hand, the overlap distance has strong influence on the partial hydraulic efficiencies. An increase in overlap distance gives enhancement of overtopping flow rate and hence the hydraulic efficiency of the main reservoir, while those of the lower ones is decreasing.