The invention relates to a welding machine with adjustable electric arc energy density, and the welding machine comprises a welding main machine, a gas supply system, a cooling water circulating system and a welding gun, wherein the welding gun comprises an upper insulating outer sleeve, a middle insulating outer sleeve, a lower insulating outer sleeve, a driving source, a tungsten rod regulating device, a cooling water clamping sleeve, a tungsten rod clamping sleeve, a tungsten rod, an electric arc nozzle, a protective gas nozzle, an operating handle and a control circuit; the tungsten rod regulating device comprises a rotating nut which is driven by the driving source and is limited by a limiting device; the cooling water clamping sleeve is formed by the way that an inner tube, a middle tube and an outer tube are brazed into a whole, the lower end of the inner tube is provided with a tapered bore and an internal thread which are matched with the electric arc nozzle, and a cooling water tank is formed on the outer side wall of the inner tube; the tungsten rod clamping sleeve is composed of the outer tube, the inner tube and a mandril, the outer tube is provided with the internal thread corresponding to the external thread of the rotating nut, especially an elongated slot which vertically extends for a certain length and a gas tank spirally surrounding the outer tube are arranged at one side close to the upper end of the outer tube, and the lower end of the elongated slot is communicated with the spiral gas tank to form a compression gas tank. The welding machine with adjustable electric arc energy density provided by the invention has the advantages of simple structure and convenience in operation.