There are two models, LHA gantry type automatic welding machine and LHT double column-beam 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. LHT double column-beam automatic welding machine can weld two pieces of beam at the same time, and the web height of beam is not limited by main machine.