Corrosion of the TiO2 coatings which were exposed to seawater for different time periods were measured with electrochemical impedance spectroscopy（EIS），and their microstructures were investigated with SEM in order to study the corrosion failure process.The results were that the polarization resistance of the TiO2 coatings (a measure of corrosion prevention)dropped sharply at first，and slightly increased to a stable value due to blocking of corrosion product and filths.An appropriate equivalent circuit was established to analyze the EIS，and the change of the parameters of elements in the equivalent circuit were tested in order to analyze the failure mechanism of TiO2 coatings.