Abstract: By means of mechanical properties testing, SEM and XRD, the effects of yttrium element and solid-solution on the microstructure and mechanical properties of AZ31 magnessium alloy were discussed, and the fracture ways were analyzed. The results show that the rare earth element Y could refine as-cast α-Mg matrix microstructure and had good fine grain strengthering effect on the magnesium alloy. The compound Al2Y, formed by Y and Al, while in addition to strengthen the grain refining, distributed uniformly on the grain boundaries, strengthened the grain boundaries, and improved mechanical properties of the alloy. The mechanical properties of the alloy were best when the content of yttrium element was 1.0wt%. The microstructure of AZ31 magnesium alloy with 0.5wt% yttrium could be most uniform after solid-solution treatment at 440 ℃ for 10 h. Fracture way of the alloy with yttrium element was ductile rupture combining with cleavage fracture.