Abstract: A metal inert gas( MIG) welding system was rearranged,for vertical surfacing welding,in which the arc was stably burned between a tungsten electrode and a welding wire. Influences of welding current,welding speed and the distance between the tungsten electrode and the workpiece on weld formation were analyzed. The microstructures,microhardness,tensile and impact properties of the overlaid coating were analyzed. The results showed that,compared with the traditional vertical welding,the weld seam has advantages such as good appearance,no macro defects,small spatter and high welding efficiency. Microstructures of the overlaid coating mainly consists of pro-eutectoid ferrite,side strip ferrite and acicular ferrite. Hardness of the overlaid coating is higher than that of the base metal. The tensile and impact properties meet the standard requirements.