Using a new semi-solid preparing and rheoforming machine which self-developed for light alloys in laboratory,researched effects on technology to alloy microstructure,such as shear temperature,shear speed rate,pressure force.The results show that shear not only changed the shape of α-Mg,but also changed distribution of the phase,namely α-Mg and β-Mg17Al12 eutectic structure due to grain refinement lixiviation tend to intergranular distribution equably,almost forming continuous mesh texture around α-Mg grain;the shape of semi-solid particles becomes regulate quietly,and average distribution in alloy body under high shear speed rate;the solid-phase rate of alloy structure becomes higher,and the solid-phase particles become also fine when shear temperature is low;when semi-solid AZ91D alloy is cooling and forming,applied to proper force make for structure refinement and advanced properties.