The effects of two-stage solution treatment and aging on the microstructure and properties of an extruded Al-8.2Zn-2.0Mg-2.3Cu alloy were investigated using SEM, EBSD, and TEM. The results indicate that the residual second-phase particles significantly decrease after the two-stage solution treatment. Following aging, the alloy’s ultimate tensile strength, yield strength, and elongation reached (630.3±12.3) MPa、(535.9±10.9) MPa and 12.6%, respectively. A theoretical strengthening model was developed based on the primary strengthening mechanisms of Al-Mg-Zn-Cu alloys. The model calculated the relationship between tensile strength, yield strength, and the strengthening mechanisms, including solid solution strengthening, grain boundary strengthening, precipitation strengthening, and work hardening. The analysis revealed that precipitation strengthening was the dominant mechanism in the aged alloy. The relative error of the calculated tensile strength was only 0.22%, while the relative error for yield strength was 1.39%. These results closely matched experimental data, providing a theoretical foundation for the development of higher-strength Al-Zn-Mg-Cu alloys and further research into their strengthening mechanisms.