A high quality excitation system not only plays an important role in the stability of power system but also can improve the performance of generators and power system. In this paper, a PWM rectifier is applied to excitation system of synchronous generators. It improves the quality of generator’s supply by achieving low harmonic current conversion and improving high power factor transform of excitation unit. Simulation results about design system through MATLAB are presented to show the obvious effect on the inprovement of the output of generator and increase of adopting efficiency power unit.