With the multiple electrode system, the intergranular corrosion mechanism of the heat treatment strengthened aluminum alloys was investigated. The multiple electrode system simulated the situation of the grain boundary area, and the results showed that the application of the multiple electrode system was quite helpful for the study purpose. The 7075 T73 and 2091 T651 aluminum alloys were investigated in this paper. The results revealed that it is the potential differences which causes intergranular corrosion.