Al-6.2Zn-2.3Mg and Al-5.0Zn-3.0Mg alloys were prepared, and then solution-aging treatment proceeded. Based on the empirical electron theory of solids and molecules (EET), in this paper, the valence electron structures of solid solutions of alloys were calculated, and then the effect of Zn/Mg on aging-precipitation behavior of Al-Zn-Mg alloys was studied. It is shown that solid solution a-Al-Zn-Mg prior formed during solid solution of Al-6.2Zn-2.3Mg alloy provides the condition for the formation of GP Zone of h precipitation sequence. Only h precipitation sequence is started, so aging-hardening behavior of Al-6.2Zn-2.3Mg alloy appears obvious two peaks characteristic. While the two solid solutions a-Al-Zn-Mg and a-Al-Mg-Zn-Mg-Al formed during solid solution of Al-5.0Zn-3.0Mg alloy provide the condition for the formation of GP Zone of h and T precipitation sequence, respectively. These two precipitation sequences have so many different at aging progress, precipitation time and their strengthening effects of strengthening phases, transforming time and caused strengthening effects weakness of strengthening phases, so these two precipitation sequences of h and T are started when aging, aging-hardening behavior of Al-5.0Zn-3.0Mg alloy does not appears obvious two peaks characteristic.