H-beam automatic assembly machine works as follows: The preferred cutting machine is cutting the steel plate (flange plate, web) flat after hanging input into the assembly machine rollers, clamping device consists of three groups of assembly machines the flange and web positioning initially clamped by the active input roller workpiece enter the host, the host has adjusted the web, web benchmark size, to be precise positioning of the workpiece on, open the automatic cycle button, welding head can be positioned, and then the good point with a crane hanging from the H-beam assembly machine after entering the automatic submerged arc welding processes.