The effect of heat treatment on Microstructure and properties of Mg-11Gd-2Y-3Sm-0.5Zr alloy was studied though the method of alloy preparation, mechanical properties test and microstructure analysis. The results showed that the second phase disappeared gradually with the solution time increasing, the hardness of the alloy decreases rapidly, and then tends to be stable. As aging time increasing, dispersed second phase precipitates in the alloy, and the hardness of the alloy reached a peak value at 12h. The tensile strength of the aged alloy was increased by 44% compared with the as cast state, the elongation at break increased by 25.4%.