To investigate the fundamental relationship between corrosion rate and magnetic induction surrounding steel reinforcement, an innovative magnetic-based corrosion evaluation apparatus has been developed, which can be directly embedded inside reinforced concrete structures to monitor the corrosion rate of reinforcement. Preliminary calibration results show that the mass loss of corrosive reinforcement has a linear relationship with the voltage increment detected by Hall-effect sensor due to the variation of magnetic induction surrounding the corroded reinforcement. Subsequently, an experiment on the reinforced concrete beam subjected to chloride solution coupled with external loading has been conducted. Magnetic technique, half-cell potential measurement and acoustic emission detection have been utilized simultaneously in the experiment to monitor the corrosion process of reinforcement. The experimental results from the aforementioned techniques demonstrate good consistency. Especially, the magnetic corrosion monitoring device proposed in this study has the good capacity of quantitative analysis of corrosion rate.