This paper deal with the investigation of the effects of opening ratio of airflow control valve for dual duct OWC chamber system. The system contains OWC chamber and dual duct. One duct is used for installing the energy-converting device and other one is for control the flow rate using flow control valve. The performance of energy converting device can represented by the free surface elevation inside the chamber and bi-directional air velocity in the duct. The airflow control valve is use to control the air velocity against the difference proposed site incident wave conditions. The effects of opening ratio of control valve at the flow control duct have investigated using experimental methods. The wave elevation inside the chamber, the pressure difference and air velocities in the both of duct have measured to predict the pneumatic power of OWC system. A relationship between opening ratio of flow control valve and airflow rate has investigated in the dual duct OWC system.