Real time monitoring of corrosion of rebar in concrete was conducted, electrochemical method is the simplest method for monitoring corrosion of rebar in concrete. This method is simple in a varying environment and can monitor the corrosion of rebar in a long term. It not only can monitor the rebar corrosion rate, but also can test the long term corrosion quantity. By measuring the polarization resistance regularly, the corroded quantity of rebar can be estimated within a certain time interval.