Abstract: By adjusting Mg element content in Al-Zn-Mg-Cu-Er-Sc-Zr alloy, the influence of the change of the Zn/Mg ratio on the phase evolution and corrosion performance of the alloy was studied. The results show that Al₈Cu₄Er phase, Al₃(Er,Sc) phase and Fe-containing phase have an obvious concomitant relationship, and they both depend on the Fecontaining phase to grow. The change of the Zn/Mg ratio can significantly change the interaction between the three. A high Zn/Mg ratio is conducive to the independent growth of the rare earth phase, and under the condition of the ratio of 4.18, the Al₈Cu₄Er phase and Fe-containing phase significantly refine. The refined grain boundary second phase makes the corrosion pit depth only 82 μm, while the continuous associated mixed phase and coarse rare earth reduce the corrosion resistance of the alloy to different degrees.