An oscillating water column (OWC) device is a promising wave energy converter (WEC) to utilize ocean wave energy resources. The OWC chamber absorbs the kinetic energy of ocean waves and converts the water column motion to reciprocating airflow. A power take-off system (PTO-system) of the OWC-WEC consists of an air turbine, generator, and power control system. An airflow drives an air turbine, which rotates a generator to produce electricity. The air turbine induces a pressure fluctuation due to its aerodynamic characteristics, which directly affects the fluid motion inside the chamber. In this study, the wave energy conversion problem of the OWC-WEC was discussed based on the experimental and numerical simulation results, considering the turbine-chamber interaction. The wave energy conversion problem from wave to power was solved using the finite element method (FEM)-based numerical wave tank in the time domain. The air turbine was numerically modeled based on aerodynamic coefficients and inertia properties. The validity of the present numerical method was examined by comparing it with the experimental results conducted in a two-dimensional wave flume at the Korea Research Institute of Ships and Ocean Engineering (KRISO). The effect of the turbine-chamber interaction on the energy conversion performance was investigated regarding the various rotational speeds of the air turbine based on experimental and numerical analysis. It was observed that the rotational speed conditions of the turbine, where the hydrodynamic performance of the OWC chamber and the aerodynamic performance of the turbine could be maximized, were different from each other. Therefore, it can be seen that a control technology considering the combined performance of the chamber and air turbine is required to maximize the energy conversion performance of the OWC-WEC.