The invention discloses a welding machine water tank, which comprises a water tank body, wherein the water tank body is made of PE (poly ethylene) plastics, the size of the water tank body is 187*250*390mm, the thickness of the water tank body is 3 to 4mm, screw nuts used for fixing the welding machine water tank onto a welding machine are internally embedded at the outer surface of the water tank body, the water tank body is provided with a water filling opening and a water tank cover matched with the water filling opening, the water tank cover is lined with a waterproof sealing gasket, air outlet holes are arranged in the water tank cover, the bottom of the water tank body is provided with water outlet holes used for realizing the water circulation, and the welding machine water tank also comprises a filter net used for filtering liquid impurities during water adding. The welding machine water tank provided by the invention has the advantages that the occupied size is small, the water storage quantity is greater, the circulation effect is better, durability is realized, the welding machine water tank is suitable for being conveniently installed on a welding machine casing, the structure is simple, the use is convenient, and the practicability is high.