Abstract: The extruded Mg-2Zn-0.5Y alloy was subjected to cryogenic treatment at different time. The effects of cryogenic treatment at different time on the microstructure and tensile properties of Mg-2Zn-0.5Y alloy were studied by OM, SEM, XRD and tensile test.The results show that the microstructure of as extruded Mg-2Zn-0.5Y alloy is mainly composed of α-Mg and a small amount of W phase.With the increase of cryogenic time, the grain size of Mg-2Zn-0.5Y alloy has no obvious change, and the precipitation amount of W phase increases gradually.The volume fraction of W phase in Mg-2Zn-0.5Y alloy is 5.33vol% after cryogenic for 12 h. Cryogenic treatment has no obvious effect on the tensile strength of Mg-2Zn-0.5Y alloy, but can significantly improve the plasticity of the alloy.The elongation of Mg-2Zn-0.5Y alloy after cryogenic treatment for 1 h is 17.4%, which is 142%higher than that of extruded alloy.