In this paper, the microstructures and mechanical properties of extruded Mg-6xZn-xY alloys at the extrusion ratio of 81:1 are quantitatively investigated. The results show that I-phase content gradually increases, the average grain size of α -Mg matrix decreases first and then increases, with the increasing Zn, Y content. The α -Mg average grain size of Mg-6Zn-1Y alloy is minimum of 2.9 μm, and the size distribution is most uniform, the standard deviation of α -Mg grain size also reached the minimum of 0.77 μm. With increasing Zn, Y content, yield strength and tensile strength of Mg-Zn-Y alloy increase, and elongation decreases. Compare with α-Mg grain refinement, the content of fine I-phase increases significantly to improve the strength of Mg-6xZn-xY alloy.