In this paper, an Al-8Zn-3Mg-1.05Cu alloy was designed according to the solid solubility of Zn, Mg and Cu elements in Al. The hot-rolled plate was subjected to solid solution treatment. The results of SEM and XRD showed that the solid solution structure with only a small amount of compound residue was obtained after solid solution treatment. Further cold rolling, annealing and aging treatment of the alloy were carried out. The EBSD results after cold rolling and annealing showed that the alloy obtained incompletely recrystallized structure after cold rolling and annealing. The KAM diagram showed that the dislocation density in the structure was high. The tensile properties of the alloy after annealing are fine, and the yield strength and elongation are 458.61 MPa and 15.6 %, respectively. The TEM results after aging treatment showed that a large number of fine MgZn₂ phases were precipitated in the microstructure. The size of MgZn₂ phase is small, and the average size is about 6.40 nm, which is smaller than the size of MgZn₂ precipitates in the reported alloys. After aging, the alloy obtained ultra-high strength and good plasticity, the yield strength and elongation were 729 MPa and 10.37 % respectively. The strength composition of the alloy was calculated, and the precipitation strengthening contribution value of the fine MgZn₂ phase was 348 MPa. The calculated yield strength value matched well with the experimental value.