The invention discloses a water tank for a welding machine. The water tank comprises a water tank body. The water tank body is made of a PE plastic material, the dimension of the water tank body is 190*250*390 mm, and the thickness of the water tank body is 5 mm. Nuts for fixing the water tank for the welding machine to the welding machine are embedded into the outer surface of the water tank body. A water injection opening and a water tank cover matched with the water injection opening are arranged on the water tank body. A waterproof sealing washer is arranged in the water tank cover in the form of a lining. A vent hole is formed in the water tank cover. Water drainage holes for achieving water circulation are formed in the bottom of the water tank body. The water tank further comprises a filtering screen for filtering liquid impurities when water is added. The water tank for the welding machine is small in occupied space, large in stored water amount, better in circulating effect, durable in use, simple in structure, convenient to use and high in practicability and is suitable for being mounted on a machine shell of the welding machine conveniently.