In order to study the high-temperature rheological behavior of Mg-Gd-Y-Zn-Zr alloy, hot tensile tests were carried out on Gleeble-1500 thermal simulation testing machine at deformation temperature of 250~400 ℃ and strain rate of 0.001~1 s-1. Considering the effects of temperature, strain rate and strain in the high-temperature deformation process, an improved Johnson-Cook constitutive model of Mg-Gd-Y-Zn-Zr alloy was established. The experimental results showed that the flow stress of the Mg-Gd-Y-Zn-Zr alloy had a nonlinear relationship with the deformation temperature, strain rate, and strain. The increase of the strain rate and the decrease of the deformation temperature would cause the flow stress of the alloy to increase significantly. The average relative error (Δ) between the predicted data of the improved Johnson-Cook constitutive model and experimental data was 4.5%, and the correlation (R) was 0.994. The established constitutive model could accurately describe high temperature rheological behavior of Mg-Gd-Y-Zn -Zr alloy.