Wave energy can be converted into electrical energy by using a wave energy converter. The oscillating water column (OWC) based wave energy converter is one of the most useful device because of its simple structure and easy handling features. The water column in an air chamber oscillates in accordance with the surrounding ocean wave, and results in an alternating airflow inside the chamber. The airflow then rotates an air turbine connected to a generator. The authors have developed an impulse turbine that rotates to the perpendicular direction of alternating airflow. The turbine has two rows of guide vanes, and one rotor between them. The blade profile is formed by the combination of a circle and an ellipse. In the present study, a simple turbine cascade was employed as a purpose of reducing the manufacturing cost, and the performance of turbine with simple cascade was investigated using the computational fluid dynamics (CFD) analysis. Results are compared with the experimental data.