Oscillating water column (OWC) systems are commonly used as wave energy converters. Such a system consists of an air chamber with a seawater inlet and an air discharger. If seawater moves as a result of the vertical motion of external waves, then the seawater within the OWC moves as well. This movement within the system generates air pressure, which produces power with which to turn the Wells turbine in the air discharge port. OWC systems must be designed in consideration of vibration because waves possess basic oscillation properties. In this research, the efficiency characteristics of OWC systems combined with breakwaters are studied by applying a vibration model. Factors affecting the energy conversion rate of OWC include the volume of air in the air chamber, pressure, and wave period. In this study, changes in the energy absorption efficiency of OWC are measured according to the area ratio between the air discharger and the air chamber, as well as on the basis of air chamber length. Simulations are performed with varying design parameters, such as internal wave, air pressure, and energy, according to changes in external waves. In addition, wave period properties are modified according to the surroundings of the sea in which the OWC system is installed. Variations in these period properties affect energy conversion efficiency. Therefore, changes in energy absorption efficiency due to the wave period are simulated in this study to design an OWC system with high absorption efficiency in view of the characteristic of wave periods in Korea.