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In this paper, Al-30Zn-3Cu-2.5Si high Zn Al-based alloy is taken as the research object, the effect of Er and Zr on the microstructure and mechanical properties of as-cast and heat-treated alloys is investigated, and the action mechanism is analyzed and discussed. The results show that the grain size of the alloy can be obviously refined by adding 0.10 wt% Er and 0.10 wt% Zr, the average grain size is reduced from 74.28 μm to 60.01 μm, and the grain size of α-Al is changed into fine equiaxed grains. The addition of rare earth elements Er and Zr can form fine particles of Al3(Er, Zr) in the alloy and pin dislocations to improve the mechanical properties of the alloy. After adding Er and Zr, the tensile strength of as-cast alloy increased from 323.01 MPa of alloys without addition of Er and Zr to 358.29 MPa, and the tensile strength increased by 10.93%; and the yield strength increased from 309.33 MPa to 315.00 MPa, and the yield strength increased by 1.83%; the elongation has not changed basically. The tensile strength and yield strength of the alloy strengthened by solution-aging heat treatment are 449.48 MPa and 408.51 MPa respectively, which are 25.45% and 29.68% higher than those of the as-cast alloy. The coarse second phase exists at the grain boundary, which results in the poor elongation of the alloy.