The auto-welding machine for H-type steel accepts the AC frequency converter to control speed with the merits of stable and reliable running and quick returning. It uses the auto-arc tracing and centering device to ensure the welding gun being auto and correct centering to the target workpiece. Meanwhile, it is equipped by the auto welding flux feed and recovery system, easy operating and high efficiency. The column-beam welding machine can increase the height of web plate according to the need of users.