Abstract: The corrugated floor of a certain stainless steel vehicle body underframe is a double-layer structure. The upper layer is a 0.6 mm thick stainless steel corrugated plate, and the lower layer is a 0.6 mm thick stainless steel flat plate.The lower stainless steel plates are in a lap structure and are connected by continuous seam welding to ensure their sealing. The upper stainless steel corrugated plates are placed over the lower stainless steel plates and connected by intermittent seam welding. Both the corrugated plate and the plate are thin plate structures that are prone to deformation. During the welding process of the corrugated floor, when the corrugated plate and the plate are not in a tight fit state, under the squeezing action of the upper and lower electrode wheels of the welding equipment, the corrugated plate and the plate are displaced and misaligned, gradually forming a serious bulging defect, resulting in the scrapping of the corrugated floor, not only affecting the day’s production tasks but also significantly increasing production costs . This paper presents a new process method that can ensure product quality and effectively reduce production costs aiming at the severe bulging defect that is prone to occur in the seam welding process of this composite structure corrugated floor.