Abstract: An investigation of dissimilar metal joining between AZ31 B Mg and 6061 Al by CMT（ Cold Metal Transfer） welding was conducted. To achieve successful welding of Mg-Al dissimilar metals,hot-dip galvanized steelplate of HDG60 was selected as transition metal,AZ61 and 4043 welding wires were utilized in welding process of Mg-steel and Al-steel,respectively,and different welding parameters were used on each side. It is shown that the heat input is controlled effectively and the interface reaction layer is thin via CMT welding. The vacancy of brittle Al₃Mg₂ and Mg₁7Al₁2 intermetallic compounds during the direct welding of Mg to Al can be attributed to the appropriate selection of transition metal. The mechanical properties of the welded joint were optimized because MgZn,FeAl₃ and Fe₂Al₅ phases with smaller thickness are mainly formed on the welded joint interface. For example,the tensile strength is higher than 180 MPa and the elongation is good with regard to the CMT welded joint of Mg-Al dissimilar metals,which indicates that the Mg-Al dissimilar metal can be joined effectively by means of the transition metal.