Abstract: Aiming at the operation of direct drive wave power system under complex working environment, the model mismatch is fully considered, a sliding mode observer is designed to detect the modeling error online, and the system identification technique is applied to fit it, and reduce the amount of online computation. The transfer function was converted into state space, and more accurate hydrodynamic equations were established to design subsequent strategies and reduce the influence of model mismatch; Based on the Variational method, the energy functional is constructed, and the optimal control law is obtained after solving the extreme value of the functional, the velocity of the system is obtained by filtering estimation and the ideal current is tracked and controlled by the Space vector pulse width modulation（SVPWM） to improve the power capture ability of the power generation system; The simulation results show that the proposed scheme has good dynamic performance, strong robustness and high observation accuracy, which can effectively improve the wave energy capture ability of the system with modeling errors, increase the output energy and increase the average output power.