Abstract: Mg-3Si-4Zn-xNd magnesium alloys with different Nb contents were prepared by adding modifier Nd to Mg-3Si-4Zn magnesium alloy.By observing the microstructure changes of primary and eutectic Mg₂Si, the influence of modifier Nd on the microstructure of Mg₂Si was explored.Through the test, the effect of the change of Mg₂Si phase on the hardness of the alloy was explored.The results show that the modifier Nd has a good effect on both the primary and eutectic Mg₂Si.When the Nd content is 2.5%, the best metamorphic effect is obtained.The primary Mg₂Si changes from a coarse dendritic structure with an average area of about 600 μm² (40 μm×15 μm)to a fine and irregular structure with an average area of about 139 μm² polygonal bulk structure, eutectic Mg₂Si changes from a complex Chinese character shape with an average area of about 444 μm² to a simple Chinese character structure with an average area of about 145 μm².The hardness of the alloy reaches the maximum value, increasing from 58.75 HV0.1 to 73.27 HV0.1, increasing by 24.7%.