The 7075 Al-alloy was subjected to T6 aging treatment at deep cryogenic temperature (DCT-T6) via soaking in liquified nitrogen, and its precipitation phase, dislocation density and tensile properties were assessed by means of TEM, SEM and tensile testing techniques. The results show that the DCT-T6 could increase the density of intra-grain precipitated phases, reduce the size of precipitated phase, increase the dislocation density and the formation of sub-grain, in comparison with the conventional T6 treatment. In the range of 3~6 h, with the increase of soaking time, the η' phase density increases and then decreases, and the inflection point is 4 h; the size of grain boundary precipitated phase (GBP) and the phase spacing, the number of linear defects, η phase density, dislocation density and the number of sub-grains all increase constantly; the tensile strength of the alloy increases and then decreases, and the elongation constantly decrease. When the soaking time was 4 h, the tensile strength of the alloy reached a maximum value of 645 MPa, which was 13.1% higher than that of the T6 alloy; when the soaking time was 3 h, the elongation of the alloy reached a maximum value of 13%, which was 44.4% higher than that of the T6 alloy.