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Hot deformation behavior and microstructure evolution of a new high strength Al-Zn-Mg-Cu alloy were studied in a temperatures range of 300~450 oC, a strain rates range of 0.001~10 s-1, and a reductions range of 30%~80% by high-temperature compression tests. Characteristics of stress-strain curves were investigated. Kinetics analyses indicate that the stress exponent and hot deformation activation energy are 4.97 and 150.07 kJ/mol, respectively, suggesting that deformation would be controlled by diffusion mainly. Microstructure observation by OM shows that precipitates in the deformed grain dissolve into the matrix and microstructure in the deformed grain become homogeneous gradually at higher temperatures or lower strain rates, while the prior coarse grains elongate along the deformation direction, and coarse un-dissolved phases at grain boundaries become smaller and more dispersive at the same time. The results of TEM and EBSD show that microstructure evolution during hot deformation of the alloy is characterized by generation and formation of sub-grains, and mechanisms of microstructure evolution during hot deformation is dynamic recovery and geometric dynamic recrystallization at large reductions.