Conventional Corrosion testing, either the salt spray test or the salt water immersion test , is a very time consuming process and often taking dozens of days. The aim of this study is to quickly screen for poor corrosion resistance of polyester powder coating on aluminum alloy. It was found that the coating with poor corrosion resistance quickly degraded in 4 days by the galvanic effect produced by the graphite coupling with the coated specimen in the salt water. In the process of coating degradation, the indicators of AC impedance as well as the coupling potential obviously changed in the synchronization, so these two indicators can be used as an important basis for coating degradation monitoring technique. By comparison, the coupling potential measurement is more convenient for real time corrosion monitoring of coating.