In this paper, the author successfully fabricated Mg-Sr and Mg-Sr-Y alloys by melting-leaching reduction method using SF6 and N2 as protected gas. The micro-structures of the alloys were investigated in details，and the results showed that dendrite α-Mg and eutectic α-Mg and Mg17Sr2 were the main phases in the Mg-Sr alloy, while Mg -Sr-Y alloys were composed of dendrite α-Mg and small eutectic α-Mg and Mg17Sr2 and tiny Mg24Y5. More eutectics were distributed around dendrite crystals in the Mg-Sr alloy, the Mg17Sr2 with aspect ratio of 6 : 1 were aligned and discontinuous lamellae, a Mg17Sr2 was irregular particles. The microstructures of Mg-Sr-Y alloy refined, Mg17Sr2 and tiny Mg24Y5 particles with size of 2-3μm distributed in the α-Mg dendrites and boundaries. The fomation and growth of both Mg24Y5 and Mg17Sr2 in the alloys were stated. It is obvious that the role of improving the heat-resistant Mg alloy of Mg24Y5 is more than Mg17Sr2.