In order to improve the understanding of the effectSmechanism of rare earth yttrium (Y) element on the plastic deformation of as-cast ZK30 magnesium alloy, and to use it more effectively, carried out a series of isothermal compressive tests of specimens were performed in the deformation temperature range of 573~723 K, and the strain rate range of 0.001~1 s_-1 on thermo-mechanical simulator. Combing with the microstructure observation, the effects of Y (1.5wt %) on the microstructure, flow behavior, constitutive parameters and high temperature plastic properties of the ZK30 magnesium alloy were investigated. According to the hyperbolic function, constitutive parameters of the alloy were obtained by linear fitting, a nonlinear flow model and its constitutive equation have been established and employed for studying the plastic deformation behavior and the relationship between temperature, strain rate and flow stress. The results showed that Y could refine the as-cast grain and increase the amount of eutectic intermetallic compound in grain boundaries. The Y doping could effectively enhance the flow stress level and peak stress, but the change trend of true stress-strain curves are less affected. The average activation energy (Q=181.082KJ.mol_-1) and stressSexponent (n=5.778) for the plastic deformation have been determinded, enlarged by 14.2% and 21.6%, respectively. The resultsSshow that theSplastic deformationSresistanceSof theSalloySis enhanced. Combined with metallurgy microstructure of these samples after deformation, Y could refine the grain and increase the amount of the dynamic recrystallization in triangle boundaries. The results showed that Y was facilitatingSdynamicSrecrystallization occur, and it was influencing theSmechanism of interface migration.