X-ray Pipe Crawler is the welding seam detection device that widely used in Oil pipeline construction of middle and far distance transmission. In this paper, a method of automatic positioning system used in pipe crawler weld by using DSP is introduced. And investigate the base method of seam image process. The design of an automatic positioning system used in pipe crawler weld based on TMS320DM642 is given. The image edge detection simulation system experiments are based on MATLAB.