In order to stabilizing terminal voltage of a generator, this paper designs two excitation controller improved from the PID based on nonlinear control and fuzzy control theory. Then, simulation results of three excitation controllers in SIMULINK are compared in different disturbance and faults such as terminal voltage step, mutant Load-shedding, one-circuit broken and three-phase short circuit. Simulation results show that: three excitation controllers achieve the goal that stability of terminal voltage is maintained. And PID +Fuzzy excitation controller has the better robustness than the others.