Magnesium alloy is a light alloy material with potential applications,but many problems need to be studied for it.In the experiment the process of solidification and the microstructure of magnesium alloy under the effect of magnetostatic field was studied.Some phenomena were found that the microstructures of magliesium alloy were changed obviously:the thickness of grain boundary was reduced，the content of solute in the grain was increased apparently and reduced slightly in the grain boundary.The analysis showed that urlder the effect of magnetostatic field the microstructure of magnesium alloy was improved，and this has great significance to improve the propenies of magnesium alloy.