Abstract: The effect of Cu content in the 6005A aluminum alloy used for high-speed trains on its electrochemical behavior was investigated by electrochemical impedance spectroscopy(EIS), immersion test and polarization curves. The results showed that a proper Cu content can improve efficiently the compactness of the alloy's surface oxide films. When the Cu content is 0.4%, the reactive resistance Rct due to corrosion as shown on the electrochemical impedance spectroscopy of 6005A increases and the double-layer capacitance Q2 decreases, and the polarization curve exhibits an anode passivation zone in a wide range of potential. However, the alloy's self-corrosion density increases slightly, which means that the corrosion resistance of the alloy decreases. Moreover, the immersion test for the alloy immersed in the 3.5% NaCl solution revealed that the pitting corrosion, intergranular corrosion and exfoliation corrosion occur sequentially on the alloy. The main influence factor on the corrosion resistance of the alloy is the compactness of its surface oxide film.