The mechanical properties of Al-Zn-Mg aluminum alloy were improved by deformation strengthening and transformations strengthening adopting thermomechanical treatment, whose process are solution treatment, preageing treatment, deformation treatment and ageing treatment in turn. The paper focuses on the influences of deforming degree and ageing process on microstructure and properties of Al-Zn-Mg aluminum alloy. The experimental results show that hardness increased with increasing deformation ratio, and the value are greatly higher than that of samples after solution treatment. The results of ageing after deformation show that the hardness enhanced with prolonging the ageing time, which reach the peak value at 16 hours. In addition, the microstructure became more homogeneous and the grain was refined obviously by metallography microscope observation. The second phase precipitate dispersedly to strengthen the alloy. Above all, in order to obtain the better mechanical properties, the optimal thermomechanical treatment processes are solution treatment at 470°C for 2h, preageing treatment at 140°C for 24h, deformation with ratio of 40% as well as ageing at 120°C for 16h.