A large amount of coarse Chinese-script-like Mg2Si particles in the magnesium alloys containing much silicon is harmful to the mechanical properties of the alloys. Sr and Nd were added in Mg-9Al-1Si-0.3Zn alloy to refine the coarse Mg2Si, and the effect of the added elements on microstructures and mechanical properties of the alloy were studied. The refining mechanism of Sr and Nd to Mg2Si was analyzed. The results show that the Chinese-script-like morphology of the Mg2Si particles is improved and uniform polygonal block are formed with the addition of Sr element. When the Sr addition is 0.16 wt%, the particles appear in a completely polygonal morphology. When both Sr and Nd elements are added to the alloy, an intermetallic compound of Mg, Al, Nd and Si elements precipitate; the more added Nd, the more new phases, which act as the heterogeneous nuclei for the growth of the Mg2Si particles. The Mg2Si particles are refined as an irregular shape under the combination effects of Sr and Nd elements. The grain-refinement on Mg2Si particles improves the mechanical properties of the alloy.