There are two models, gentry automatic welding machine and T gantry automatic welding machine. It adopts A.C. Inverter control with functions of stable running and fast traveling speed. The seam-tracking arc-guide mechanism is three-spindle system to guarantee the alignment without aberrancy. The main frame and welding machine are integrated control. With flux auto-recovering system and it is easy to operate with high efficiency. T gantry automatic welding machine can weld two pieces of beam at the same time, and the web height of beam is not limited by the main machine.