This study uses the finite difference software, FLOW-3D, to develop a numerical model to simulate the hydrodynamic characteristics for Oscillating Water Column (OWC) caisson breakwaters. The numerical model is verified by a flume channel experiment for the interaction mechanism between air and water. Through the analyses with different incident wave parameters of the OWC caisson breakwaters, the following parameters are evaluated as energy capture efficiency indices: the amplitude magnification (a/a(0)), the air velocity at the orifice (V-ori), the air oscillation pressure (H-p), the hydrodynamic efficiency (eta(h)), the energy produced by air for a period (E-air), and the average power produced by the air (P-air). The results show that the optimal dimensionless wavelength ratio (L/l(c)') for the optimal hydrodynamic efficiency (eta(h)) is different from the optimal dimensionless wavelength ratio (L/l(c)') for the average power produced by the air (P-air), the amplitude magnification (a/a(0)), the air velocity at the orifice (V-ori), and the air oscillation pressure (H-p). For power generation purpose, this study suggests that the relationship curve between the dimensionless wavelength ratio (L/l(c)') and the average power produced by air (P-air) can be used to determine the optimal range for wave energy capture and to design the optimal size for the OWC caisson breakwaters. Under the incident wave conditions of maximum average power produced by air, the lateral force and the base moment has enlargement phenomenon. (C) 2016 Elsevier Ltd. All rights reserved.