The shrinkage defects in Mg alloy die casting were examined. Occurrence of surface and internal fissure was attributed to delamination filling during the ejection of diecasting with the asynchronism of the solidification shrinkage. Axial shrinkage porosity involves in feeding characteristic a casting with various wall-thickness and pressure holding time. The measures and suggestions for preventing or eliminating defects from Mg alloy diecasting were put forward.