The　structure　of　dissimilar　Mg　alloys　has　broad　applications　in　aerospace,　transportation,　and　other　fields,　but　welding　defects　in　conventional　welding　of　dissimilar　Mg　alloys　greatly　reduced　the　performance.　This　research　focused　on　enhancing　the　mechanical　properties　of　dissimilar　AZ61-AZ31　Mg　alloys　by　adding　Cu　interlayer　during　pulse　current　assisted　friction　stir　welding.　The　overall　hardness　was　increased　by　33%;　the　tensile　strength　was　significantly　improved,　an　increase　of　102　and　90.53%　for　AZ61　and　AZ31,　respectively.　The　grains　were　refined　with　increasing　pulse　current　from　100　to　400　A;　the　grain　orientations　were　more　random;　the　distribution　range　of　Cu　interlayer　increased　and　became　more　uniform;　the　strengthening　phases　(MgCu2　and　Al2Cu)　were　dispersed.　The　pulse　current　has　improved　fluidity　of　material;　pulse　current　has　provided　enough　energy　for　dynamic　recrystallization　and　a　temperature　condition　for　precipitation　of　strengthening　phases　with　a　uniform　distribution.　Therefore,　the　enhanced　mechanical　properties　were　attributable　to　fine　grain　strengthening,　precipitation　strengthening,　and　uniform　distribution　of　Cu　interlayer.