The corrosion behavior of Al-RE coating in copper accelerated acetic acid salt spray test (CASS) was studied by electrochemical impedance spectroscopy (EIS). Typical EIS spectral changes were clearly observed during the CASS process. The EIS was shown to be a very useful tool for studying corrosion resistance mechanism. Scanning electron microscope and X-ray energy dispersive spectroscopy were used to analyze the microstructure of Al-RE coatings before and after CASS test. The results revealed that the corrosion behavior of Al-RE coating could be divided into two different stages. In the first stage of CASS, there were two capacitive impedance semicircles in the complex plane plots. The high frequency semicircle responded to barrier layer, the low frequency semicircle responded to the electrochemical reaction of Al-RE coating. In the second stage of CASS, porous layer began to influence the electrochemical behavior.