Magnesium　alloy　arc　additive　has　fast　thermal　conductivity　and　irregular　crystallization　in　the　process　of　cold　metal　transition　welding　(CMT)　arc　additive,　and　easily　forms　obvious　holes　at　weld　seam　joints　and　rough　surfaces　of　the　formed　parts.　The　research　on　defect　control　of　repair　layer　is　of　great　significance　to　the　development　and　practical　application　of　magnesium　alloy　additive　manufacturing　repair.　The　research　results　show　that　CMT　rapid　additive　remanufacturing　of　magnesium　alloy　has　realized　lap　joint　of　multi-passes,　reproduces　the　magnesium　alloy　with　fine　grain　(~10.5　μm)　and　the　average　microhardness　is　up　to　0.89　GPa　with　high　mechanical　properties.　After　friction　stir　treatment,　not　only　the　surface　quality　is　improved,　but　also　the　holes　at　the　interface　between　weld　pass　laps　and　substrates　are　eliminated,　and　the　grain　is　further　refined　(~9.7　μm),　thus　reducing　the　risk　of　fracture　during　service.　The　feasibility　is　emphatically　verified　the　composite　manufacturing　of　magnesium　alloy　arc　cladding　and　friction　stir　processing,　and　a　new　idea　for　high-performance　magnesium　alloy　additive　manufacturing　method　is　provided.　©　2022　Journal　of　Mechanical　Engineering.