High pressure torsion (HPT) experiment followed with heat treatment were carried out on as-received Al-Zn-Mg-Cu-Zr alloy at 400 ℃ under the pressure of 1 GPa. Optical microscope, electrochemical workstation and slow strain rate tensile machine were used for microstructure observation, electrochemical corrosion and stress corrosion resistance test for the as-received and HPT processed samples respectively. The results show that HPT processing can improve the tensile strength and stress corrosion resistance by modifying the size and distribution of grains and second phases. The second phases agglomerated at the grain boundary corrode continuously, which leads to obvious intergranular corrosion and weak stress corrosion resistance of the as-received alloy. After 0.5 turn of HPT processing, the fragmentation and content reduction of second phase lead to the decrease of corrosion sensitivity, at the same time, the planar slip reduces and homogeneous slip mode increases due to grain refinement, which synthetically results in a significant improvement of the stress corrosion resistance. The HPT processed sample with 2 turns has finer grains with uniform distribution, which leads to the further increases of homogeneous slip mode compared with 0.5 turn, but under the interaction of intense pitting and stress concentration, the resistance to stress corrosion slightly decreases.