Abstract: In order to monitor the corrosion of steel bars, based on the piezoelectric ultrasonic guided wave method, active corrosion monitoring was carried out on single steel bars and steel bars in concrete that were electrically accelerated, as well as on steel bars in concrete that were not electrically accelerated, by embedding piezoelectric sensors attached to both ends of the steel bars inside the concrete. The monitoring results indicated that during the corrosion process of steel bars, the amplitude changes of ultrasonic guided wave signals can be significantly monitored in five stages of corrosion, namely passivation and depassivation, rust initiation, debonding, continued corrosion, and severe corrosion. The amplitude of the guided wave signal did not continuously decrease with the deepening of corrosion, but had a certain variation pattern. When using ultrasonic guided waves to monitor the corrosion of steel bars embedded in concrete, the corrosion stage of the steel bars can be directly distinguished by measuring the amplitude of the guided wave signal at different stages. This conclusion provided favorable data support and support for practical engineering monitoring.