In this study, the effect of the stepped sea bed on the hydrodynamic performance of an oscillating water column device is investigated using computational fluid dynamics . This investigation is performed in a numerical wave tank modeled using ANSYS Fluent, which incorporates a transient, multiphase volume of fluid method to track the air–water interface. The power take-off unit is modeled as a porous zone in the flow field to produce the pressure jump versus flow characteristics that of a real air turbine. The efficiency of the chamber with and without the stepped bottom is analyzed and compared with known results in the literature. The flow parameters such as the temporal evolution and distribution of the pressure field, velocity field and free surface are studied to understand the performance of the proposed model. The study reveals that there is an improvement in hydrodynamic efficiency with the inclusion of the stepped bottom beneath the oscillating water column chamber, which is in agreement with the previous studies carried out using analytical and boundary integral equation methods. Moreover, the computational fluid dynamics model helps to understand the flow dynamics inside the oscillating water column chamber in a more intricate manner compared to the potential flow-based studies pursued in the literature. The formation of vortices within the oscillating water column chamber, near the front wall and stepped bottom could be captured, which affects the chamber performance to a certain extent. Overall, the study could be useful in the initial design stage of shore fixed oscillating water column devices.