Abstract: A nondestructive monitoring method is developed for measuring corrosion rate of steel bar in reinforced concrete structure. This method may not be affected by the non - homogeneous distribution of the electrical signal applied to the reinforcements via a small counter electrode whose surface area is much smaller than that of the reinforced concrete structure to be tesed through properly processing the transient response of steel bar to a impressed current. Test results show that the method is reliable, which supply a possibility of on - site measurementof rebar corrosion rate.