In the traditional back-stepping excitation robust control, the main objective is the stability of the system, the control accuracy of the terminal voltage can’t be guaranteed and the optimum control of the state parameters isn’t considered. Through estimating the state parameter values of the synchronous generator by EKF and calculating the operating points of excitation system rapidly, the control accuracy of the terminal voltage of the synchronous generator is improved. Through combining the back-stepping, the direct feedback linearization and the optimum control, the optimum back-stepping robust control is realized. Simulation results of the certain excitation system show that the state parameters of the synchronous generator can be estimated by EKF, optimum back-stepping can not only eliminate the problem of the terminal voltage deviation, but also can control the convergence rate of the state parameters of the synchronous generator.