Polyaniline (Pani) on graphite electrode was synthesized electrochemically under galvanostatic condition at current density of 2.0 mA/cm2 from aqueous solution of 1.0 mol/L HCl and 0.25 mol/L aniline monomer. The Electrochemical Impedance Spectroscopy investigation of Pani was carried out at different stages of polymers oxidation. In the potential range 0.2V~0.7 V vs SCE, with the increase of test potential the membrane resistance decreased rapidly, and Faraday process at the polymer/solution interface weakened. When the test potential in range of -0.8V~0.2V or 0.7V~0.8V, the film has a higher membrane resistance, and lower ionic charge transfer resistance, which indicated that the ion exchange for the charge compensation at the polymer/electrolyte interface is much easier. And anticorrosion properties of Pani coating of different oxidations was investigated by salt spray test. The final visual observations of the tested coatings are in agree with the results of electrochemical impedance spectroscopy.