Abstract: The hyperbaric TIG welding is the most quality reliable joining method for damaged underwater pipeline.The automatic welding is the most effective way to improve the welding efficiency.The welding seam tracking algorithm is the key technology to ensure the working procedure and its quality.The specially designed CCD system is capable of working in high pressure chamber.A set of route detecting algorithm was developed.To better understanding the weld image, the histogram equalization method was used aiming at enlarging the difference between groove and other area.An outstanding image segmentation method was proposed and used to increase the target ratio and was better to the threshold selecting.A binary image edge detecting algorithm based on morphology was used to separate the welding edge and then the Hough transform was used to pick the tracking route accurately.