According to the corrosion of reinforced concrete under the combined action of chloride and sulfate attacks, some specimens of steel bar covered with cement paste layer were prepared to carry out the measurement of electrochemical impedance spectroscopy(EIS) on them immersed into chloride and sulfate solutions, and the influences of corrosion solution, water cement ratio, thickness of cement paste layer on their electrochemical parameters and the corrosion degree were analyzed. Results show that at the early period of corrosion, the surface charge transfer resistance of steel bar immersed into the combined chloride and sulfate solution is higher and the corrosion current density is lower than that in a chloride solution, so the additional sulfate in chloride solution can slow down the early corrosion process of steel bar in cement paste. But at the later period of corrosion, the surface charge transfer resistance of steel bar has an notable decrease, and the corrosion current density has a great increase, thus the additional sulfate can accelerate the later corrosion process of steel bar in cement paste. Additionally, the corrosion degree of steel bar in cement paste with high water cement ratio is higher than that with low water cement ratio, and it decreases with the increase of the thickness of cement paste layer.