Abstract: This paper introduces a realization method of microprocessor-based control for magnet exciting system of synchronous machines. The automatic measurement of magnetizing of the thyristor excitation, the strong magnet excitation by voltage feedback and the trigger of the thyristor gating circuit of three-phases controlled rectifier bridge are all monitroed by singe-chip microprocessors known as MCS-51 series. This method greatly simplifies the whole system. Experiments show that the method is very reliable.