The invention relates to a pass-type straight seam welding machine comprising a welding gun unit, a frame, an automatic centering unit, a to-be-treated material hanging unit, an automatic pushing and bracket lifting unit, a welding mandrel suspension and cylinder inner diameter positioning unit, a cylinder outer ring holding unit, a cylinder end face lifting and positioning unit, a mandrel door opening and closing unit, and an automatic cylinder incoming and outgoing unit. The whole set of machine realizes automatic feeding, positioning, welding and discharging, achieves the purpose that one person operates multiple machines, can meet welding requirements for weldments of different thickness and length, and can serve as the foundation for realizing further unmanned welding.