In this paper a visual servo control system is designed to realize the accurate tracking of the narrow butt seam of the thin plate. An effective “and” operation and statics method is proposed to reduce the image noises caused by various disturbances in the welding process. And the ROI of the image is determined to improve the efficiency of the image processing. The feature line of the thinned seam is extracted by using combination of hough transform and least square line fitting technique. Moreover the method used in this study ensured the safety and reliability. In terms of controller, to guarantee the reliability, image error filtering and output pulse verification is added to the controller. Finally, a series of experiments were conducted to verify the good performance of the proposed seam tracking system.