The corrosion resistance and mechanical properties of peak-aged AlZnMgCu alloys containing Si and Er elements were investigated with hardness test, tensile test, intergranular corrosion test, exfoliation corrosion test and transmission electron microscopy. The results indicate that peak-aged AlZnMgCuSiEr alloy is strengthened by co-precipitation of η′ phases and nano-sized GPB-II zones. The yield strength of the AlZnMgCu alloy is increased by 38.5 MPa and the elongation is increased by 4.5%. At the same time, the corrosion resistance of the AlZnMgCuSiEr alloy is enhanced due to the synergistic effect of Er and Si. The maximum intergranular corrosion (IGC) depth decreases from 264.2 to 9.9 μm. The fundamental reason is that the co-addition of Si and Er regulates the evolution of precipitated phases in grains and at grain boundaries.