Abstract: A method of autonomous seam tracking in arc robotic welding was presented.It could make the robot get rid of traditional teaching and playing back mode and automatically acquired the special coordinates of welding seam.The master computer continuously processed local area images in front of the torch in the images,which were acquired by a CCD camera,to measure the deviation between the torch and the seam and the orientation of the seam.At the same time,the computer controlled the robot to make the torch move forward along the seam and recorded the seam's coordinates in the robotic basic reference frame,which were corrected by the deviations.After the torch arrives at the endpoint of the seam,the computer controlled the robot to move the torch to the first record coordinate and begin to weld.Experiments were made on the curves seam workpieces of mild steel and aluminum alloy work pieces.The result showed that this method has good practicability.