The　microstructure　and　fine　structure　of　weld　fusion　zone　for　high　strength　fine　grain　steel　were　studied.　The　results　indicate　that　the　width　of　the　fusion　zone　is　only　20　-　40　μm　under　PC-MAG　welding　with　different　welding　parameters.　The　microhardness　is　increased　with　the　decreasing　of　heat　input.　The　acicular　ferrite　morphology　at　the　weld　side　is　affected　by　welding　parameter,　and　the　inclusions　are　located　at　the　boundaries　of　ferrite.　There　are　different　morphologies　of　carbide　in　low　bainite,　and　the　distribution　of　carbide　is　affected　by　welding　parameter.