Abstract: The hot compression deformation test of the additive manufacturing Al-Zn-Mg-Cu aluminum alloy thick plate was carried out by thermal simulation test machine（Gleeble-3500）, and the hot deformation constitutive equation of the alloy was established. The deformation temperature is 75-225 ℃, the strain rate is 0.01-10 s^-1, and the true strain is 0.693. The results show that the flow stress of Al-Zn-Mg-Cu alloy is positively correlated with the strain rate and negatively correlated with the deformation temperature. The hot compression flow stress of the alloy can be described by hyperbolic sinusoidal relationship including Z（Zener-Hollomon） parameters. The equation can be used to guide the additive manufacturing of the alloy plate. The in-situ tensile test of the additive manufacturing Al-Zn-Mg-Cu alloy plate was carried out by SEM. The results show that the cracks originate from the brittle second phase formed in the process of additive manufacturing, rather than the defect cavity. The fracture morphology of the alloy is lamellar structure formed by layer by layer printing made of additive.There are equiaxed dimples with alternating size on the fracture surface. The fracture belongs to obvious ductile fracture.