Abstract: The two-stage aging process optimization was conducted on Al-Zn-Mg-Zr alloy containing 0.25wt% scandium by orthogonal experiment. The influences of the two-stage aging process parameters (pre-aging time and temperature, final-aging time and temperature) on the mechanical properties and electrical conductivity of the alloy were studied and the microstructure of the alloy after treatment by this process was observed. The results show that the influence significance of the factors on the comprehensive performance especially mechanical properties of the alloy was ranked from high to low as follows: final-aging temperature, final-aging time, pre-aging time and pre-aging temperature. The suitable two-step aging process of the alloy was determined as pre-aging at 120 ℃ for 4 h followed by final-aging at 140 ℃ for 12 h. After treated with this process, the tensile strength, yield strength, elongation and electrical conductivity of the alloy was 553 MPa, 534 MPa, 12.0%, 37.3%IACS respectively. The η′ phase and Al3(Sc,Zr) particles distributed dispersively in the base structure of the alloy, contributing to the improvement the strength and stress corrosion resistance of the alloy.