The system simulation for a fixed O. W. C. type wave evergy absorber was proposed and have been studied. In this simulation, the form of air-chamber and turbine were refered to what was used in the real sea trial at SANZE. Since the device was fixed in very shallow water, the nonlinearity of hydrodynamic force on O. W. C. must be discussed. In this paper, the authors try to know whether equations and performances of turbine used in the system simulation are appropriate or not. Furthermore, they carry out experiments by using a small model, and consider nonlinearity of hydrodynamic forces on O. W. C. on the basis of experimental results.