SUS301L　stainless　steel　sheet　with　thickness　of　2　mm　is　welded　using　CO2　laser-metal　inert　gas　arc　(MIG)　hybrid　welding.　The　microstructure　and　phase　composition　of　joint　are　analyzed　in　detail.　Furthermore,　the　influence　of　assembly　gap　on　weld　microstructures　and　performance　is　investigated.　Results　indicate　that　the　joint　is　composed　of　fine　dendritic　structure　in　the　weld　center　and　columnar　crystals　far　away　from　the　center　zone.　And　the　columnar　crystals　are　found　growing　perpendicularly　to　the　fusion　line.　Grain　size　increases　with　the　distance　from　the　center　of　weld.　Phase　composition　in　the　joint　is　identified　as　γ　austenite　and　a　little　δ　ferrite.　The　solidification　type　of　weld　is　dominated　by　ferrite-austenite　(FA)　mode　and　the　transformation　from　δ　to　γ　is　dominated　by　massive　transformation　and　short　range　free　diffusion.　With　the　increase　of　assembly　gap,　residual　δ　content　and　tensile　strength　of　weld　decrease　gradually.　The　fracture　occurs　at　the　area　of　coarse　columnar　grain　near　the　fusion　line.