A　laser　penetration　welding-brazing　combined　with　Cold　Metal　Transfer　(CMT)　arc,　was　proposed　to　improve　weld　shape　and　interfacial　reaction　inhomogeneity　of　5052　aluminum　alloy　and　Q235　low　carbon　steel　with　ER5356　welding　wire　in　butt　joint.　The　effects　of　wire　feed　speed,　beam　offset　and　welding　speed　on　weld　shape,　interfacial　microstructures　and　tensile　strength　of　joints　was　studied.　This　method　improved　the　undercut　defect　existed　in　butt　laser　welding-brazing,　obtained　well-formed　joints　and　promoted　the　uniform　distribution　of　the　interface　reaction.　The　interfacial　intermetallic　compounds　(IMCs)　layer　consisted　of　Fe2Al5　and　Fe4Al13　and　the　thicknesses　were　controlled　to　3-5　mu　m.　Microstructures　of　weld　seam　was　composed　of　alpha-Al　and　Al3Mg2.　The　brittle　IMCs　layer　thickened　and　then　the　tensile　strength　decreased　with　increasing　the　wire　feed　speed.　The　thickness　of　the　IMCs　layer　decreased　but　weld　shape　became　worse　when　the　welding　speed　or　the　offset　increased.　The　tensile　strength　increased　first　and　then　decreased.　The　highest　tensile　strength　reached　higher　than　80　MPa　and　the　joint　fractured　in　IMCs　layer　along　the　interface.