The effects of different cryogenic treatments on the microstructure and properties of dissimilar repair welding joint of WE43 A magnesium alloy by TIG welding are studied. The results show that comparing with the as-welded,as the deep cryogenic time extends,after the deep cryogenic treatment,the grains of the dissimilar welded joints of WE43 A magnesium alloy are gradually refined and the second phase precipitates from the matrix and the grain boundary,and the microhardness of WE43 A magnesium alloy TIG welding repair joint increases,its corrosion resistance improves,the grain refinement rate can reach 54.4%,and the microhardness of weld metal zone increases by 25.3%. In general,the-100 ℃× 8 h deep cryogenic process is the best.