Abstract: There are a lot of welds between cooling tubes and mainstream tubes in radiator. These welds are plane curve with complicated shape. The plate is thin and the welding groove size is non-uniform. These result in many welding defects. To achieve automatic welding of these welds, an automatic welding machine and automatic welding process were developed. A numerical control system controlled five welding guns to move along the welding seam simultaneously. Five welding machines were controlled to work synchronously. Different welding conditions and moving tracks were adopted in different weld segments which had different welding groove shape and size. Therefore, five welds could be achieved at the same time. The quality of welds was guaranteed and the production efficiency was raised. The machine and the automatic welding process have been used in mass production of radiators.