This automatic tank welder has 5 welding strip transport methods, simulating manual strip transport, and the weld seam has a uniform appearance and is more stable. The welding seam width can be adjusted in a wide range of 0-30 mm, which can be adapted to the welding of various thin and thick plates. The welding speed, operation and power can be adjusted at will between 0-1 6 5 0 mm/min. This automatic tank welder can adjust the length and speed at will to adapt to welding at various distances.