In order to improve the power capture effect of the direct drive wave energy generation system at wave mutation, the frequency domain model of the system was analyzed. The relation curve between the system output active power and the equivalent impedance of permanent magnet linear generator in the frequency domain was exported. According to the characteristics of the curve in three dimensional space, a perturbation-observe method was proposed with alternating exerting changed step perturbation. With the changed step perturbation strategy, the system easily traps in local optimum in a wide range of maximum power point. The control strategies was proposed with changing disturbance step size according to regional slope change. The simulation system model was built in Matlab/Simulink environment. The simulation results show that the anti-interference ability of the ameliorative control strategies is improved under the mutational wave conditions, and the system can be quickly to retrack nearby the maximum power point.