Abstract: The corrosion control mechanism and corrosion rate calculation method of rebar in concrete exposed to different test conditions were studied using polarization curve and electrochemical impedance spectroscopy. The results show that, under natural corrosion condition, the corrosion reaction process of rebar was controlled by the anodic reaction. The corrosion rate can be effectively calculated utilizing a modificative equation used to calculate the bidirectional linear polarization resistance. However, under accelerated corrosion condition, the corrosion reaction process of rebar was controlled by combined mechanism of electrochemical and concentration polarization. The polarization resistance with a relatively high accuracy can be obtained by fitting the weak polarization curve. The research results provide a reference for the judgment of corrosion mechanism and the control of corrosion rate of steel reinforcement in concrete structures.