The invention relates to a plasma-arc welding device implemented by the aid of a TIG (tungsten inert gas) welding method. The plasma-arc welding device comprises an upper gun and a lower gun. An upper spray nozzle is connected with the lower end of the upper gun and is mechanically coaxially connected with the lower gun. A water cooling groove is formed in the wall of the upper gun, an upper water inlet pipe, an upper water outlet pipe and an upper gas inlet pipe are arranged in the wall of the upper gun, a flow guide component, a tungsten electrode clamp and a tungsten electrode are coaxially arranged in the upper gun, and the tungsten electrode penetrates the tungsten electrode clamp and extends into the lower gun. A water cooling groove is formed in the wall of the lower gun, a lower water inlet pipe, a lower water outlet pipe and a lower gas inlet pipe are arranged in the wall of the lower gun, a lower spray nozzle is connected with the inner wall of the lower end of the lower gun, pore passages are arranged in the center of the lower spray nozzle, the tail end of the tungsten electrode is separated from each center pore passage of the lower spray nozzle by a certain distance, and a protective cover is connected to the outer wall of the lower end of the lower gun. The plasma-arc welding device has the advantages that plasma-arc welding can be implemented, the TIG welding efficiency and the quality of weld joints can be obviously improved, and the plasma-arc welding device is low in welding cost as compared with the traditional plasma-arc welding.