The invention relates to the field of argon arc welding, in particular to a welding gun for argon arc welding. The welding gun for argon arc welding comprises a welding flux cylinder, a handle, a suction fan and a diffusion cylinder, wherein the welding flux cylinder is provided with a welding nozzle. A pipeline communicated with the suction fan through the handle is arranged on the side, away from the handle, of the welding nozzle. Sucked air is delivered into the diffusion cylinder through the suction fan. A plurality of air outlets are formed in the end of the diffusion cylinder in the circumferential direction. According to the welding gun for argon arc welding, the air, containing ozone, around the welding nozzle is sucked through the arrangement of the suction fan and delivered into the diffusion cylinder, in this way, the ozone concentration of a work zone is effectively decreased, and harm of the ozone to human bodies is reduced; a heater is arranged in the diffusion cylinder, the ozone is extremely instable in an environment at the temperature over 60 DEG C and can be decomposed into oxygen easily and rapidly, and thus an oxygenation function can be achieved to a certain extent by placing the diffusion cylinder provided with the heater in a rest room.