Abstract: The precipitation process and effect of precipitated phases at second-stage aging of 7050 aluminum alloy two-stage double peak aging were studied. The results show that the first-peak of alloy second-stage aging was hardened mainly by fine and uniform GP zone and the second-peak was hardened by fine intragranular η′phases and bulky GP zone, the strengthening effect of the latter was better than the former. The η′ phases which precipitated at peak value of second-stage peak distributed in intragranular uniformly, and η′ phases had very small spacing and large volume fraction, the GP zone was bulky. The η′ phases started to gather and coarsen then change to steady η phases with aging going along further, the GP zone disppeared.