Abstract: For problems that traditional AC voltage regulator is difficult to meet with real-time, precision regulator and voltage stabilization, an automatic control system of three-phase voltage regulating based on single-chip microcomputer was designed, realization of hardware circuit and software of the system were introduced in details. The system takes AT89C51 single-chip microcomputer as control core, can real-timely monitor change of voltage signal and achieve manual, automatic voltage regulating function according to set voltage. It also can achieve 0.01 V voltage collection precision, automatic control functions of 0-400 V boost, buck and stabilization of voltage. The experiment results showed that the system has advatages such as simple circuit, strong work reliability and high automation level.