Electrochemical corrosion behavior of HRB400 and three Cr modified steel rebars in cement extract solution with different chloride concentrations were estimated by potentiodynamic polarization curves and electrochemical impedance spectroscopy（EIS）; semiconductor properties of passivation film of the four steel rebars were studied by Mott Schottky（M S） theory. The results show that with the increasing of Cr in the steel rebar, the corrosion current density decreases, passivation interval and polarization resistance increase, and the passivation film stability is enhanced, which indicates that the corrosion resistance of steel rebar is improved. In addition, increase of chloride concentration in cement extract solution leads to increase of the corrosion current density, decrease of the passivation interval and polarization resistance, and significant increase of the carrier density, while the corrosion resistance of steel rebar is decreased. Cr modified steel rebars have higher corrosion resistance than HRB400.