This machine is the ideal equipment on automatic submerged arc welding of assembled H-shaped steel. Place the work piece on the bracket and incline by 45 degree so that its welding will be in the flat position for fillet welding operation. The welding arm equipped with submerged arc welding head can mover horizontally and vertically along the beam of gantry frame so that the welding tip on the head can be aimed at the welding seam of the work piece. The mechanical tracing device for welding seam is equipped at the front end of welding arm and the gantry frame can move straightly on the steel track for automatic welding. The machine is also equipped with flux automatic laying, recovering and treating device.