To further evaluate the corrosion conditions of steel bars in RC structures, the monitoring and location technology for the corroded steel bars in RC beams was investigated based on piezoelectric sensors. Firstly, three pairs of piezoelectric lead zirconate titanate (PZT) sensors were arranged on the surface of the steel bar, then the monitored signals were processed by Radix-4 FFT, and the frequency spectrum features were extracted to figure out the development trend of the corrosion process. Meanwhile, the applicability of the PZT-based monitoring method for the overall corrosion process of steel bars was verified. Secondly, for the purpose of locating the corrosion positions of the steel bar, the weight function of the probabilistic imaging method was modified to obtain the position image of the corroded steel bar. Finally, the peak signal in the frequency domain was analyzed, and the relationship between the damage factor (F_DI) and the corrosion rate was established to quantify the corrosion degree of the steel bar. Results show that the corrosion process of steel bars in RC beams could be divided into three phases: depassivation phase, debonding phase, and failure phase; the proposed damage factor (F_DI) could effectively depict the three phases in the corrosion process of steel bars and quantify the corrosion rate of steel bars; the probabilistic imaging method could realize whole-process monitoring and analyze the corrosion positions of the steel bars. It indicates that the monitoring technology and the probabilistic imaging method can accurately monitor the overall process and locate the corrosion positions of steel bars in RC structures. The relationship between each phase of the whole process and the damage factor (F_DI) can quantify the steel corrosion rate, which can provide technical support for the safety assessment of RC structures.