Abstract: The processing parameters of TIG repairing welding for ZM6 magnesium alloy casting were determined by testing tensile properties and X-ray.The same grain size between heat-affected zone and the base material was found by observing the microstructure of welded joints in the optical microscope and analysing micro-area composition.The element in the heat affected zone was basically occupied Mg,and the original crystal alloy elements within intragranular were migrated to the grain boundary.Weld was composed of small equiaxed crystal,the size of which was smaller than that in the base material.The grain in weld zone was also entirely occupied by Mg elements.The contents of alloying elements in the grain boundary were less than those in the base material and heat-affected zone.The crystal cracks for welding in ZM6 magnesium alloy casting were found by observing the crack location and investigating the process of welding of ZM6 magnesium alloy casting.