The hydrodynamic performance of the wave power extraction of an innovative modified breakwater-integrated Oscillating Water Column (OWC) wave energy converter is both numerically and experimentally presented in this study. The modified OWC device comprises a non-conventional perforated wall in front of a typical OWC chamber. The air-water two-fluid model, considering the fluid compressibility involved in FLOW-3D solver, is employed for the numerical simulations of the hydrodynamic characteristics of the OWC devices. The numerical simulations of the hydrodynamic performance of the OWC device are first validated by the experimental measurements with a scaled model. The effects of the geometry of the OWC chamber on the hydrodynamic efficiency are then discussed by numerical simulations using a full-scale OWC device under regular waves. The numerical and experimental results show that the present modified device can form a U-type flow pattern by the oscillating water column, thus developing better performance in extracting pneumatic power, when compared with the typical OWC device which does not have the perforated front wall. The results indicate that the present modified OWC device can not only promote the efficiency of the pneumatic power extraction, but can also reduce the wave force acting on the structure.