Abstract: The intermetallic compounds of θ(CuAl₂)、S(Al₂CuMg)、MnAl₆ and the pure Al(L1)were used to consist a multiple electrode system．This system was employed to simulate the grain boundary area of the LY12cz alloy．The mechanism of the intergranular corrosion of LY12cz alloy was studied by the electrochemical measurements,the SEM observation and the energy spectrum analysis with the simulate system．This paper confirmed the general believing that intergranular corrosion of the LY12cz alloy is caused by the formation of a multiple electrode system,which consist of the segregation of strengthening phases and the Cu-lack zone ,and locate along the grain boundaries．Besides,it is clear that in a Cl^- containing neutral solution,the S phase is the main anode which results in intergranular corrosion．Firstly,the anodic S phase dissolves,secondly the Cu-lack zone and MnAl6 dissolve gradually with the S phase still acts as a main anode．In this way,an anodic dissolution path forms along grain boundaries,causing intergranular corrosion．