The system simulation for a fixed O. W. C. type wave energy absorber has been studied. It shows both the transient states of the system while the turbine revolution becomes high velocity and linear calculation method for high velocity revolution. However, because of the radius and the number of revolutions of turbine were not optimum controlled in previous studies, both efficiencies of primary energy conversion and turbine were not necessarily optimum. This paper shows the method of optimum design for turbine on a O. W. C. type wave energy absorber. That is the optimum radius and the number of revolutions of turbine. Furthermore, in order to improve the efficiency the authors consider the system simulation with phase control and discuss the effects of phase control.