In order to study the maximum wave energy capture of the wave power generation system, the model of the oscillating buoy direct-drive wave power system was built according to the hydrodynamic equation of the buoy and the state equations of the permanent magnet linear synchronous machine. An equivalent circuit method was proposed to simulate the hydrodynamic equation of the buoy. According to random ocean wave, the wave power generation system was decomposed to multiple sinusoidal subsystem in each frequency by Fourier analysis method. The traditional control method was optimized by constructing the maximum power transmission condition for every subsystem to achieve the maximum wave energy capture. The control law was designed and the Lyapunov function was constructed by backstepping method to track the operation state of generator closely. The simulation results show that the proposed backstepping method can track the state of wave generator closely. Under random ocean wave status, the traditional control algorithm was optimized obviously to increase the conversion efficiency of the wave energy by the proposed Fourier analysis method. The maximum wave energy capture can be achieved by controlling the generator combined with the backstepping method.