Three-step aging treatments of 7055 aluminium alloy have been investigated by means of test of electrical conductivity,hardness and TEM.The results show that the first-step aging at 120℃ for 30min can play a pre-nucleating part in precipitateon of second-step aging at 190℃,when the time of first-step aging exceeds 30 min,its prolongation do not distinctly influence the electrical conductivity and hardness of three-step aged 7055 alloy.The electrical conductivity and hardness of 7055 alloy can be simultaneou.