For the laser vision seam tracking system, it is the key to extract the weld feature points quickly and accurately based on the linear structured light. Most of the existing algorithms are pixel-level feature extraction. Now an improved sub-pixel accuracy algorithm is proposed to extract weld feature points. Different from the previous algorithm, the algorithm does not need to select the threshold value. In the process of extracting the fringe centerline and detecting the feature points, the sub-pixel position was calculated first, and then the image was processed. The accuracy of the algorithm was greatly improved. Moreover, image processing mostly adopts deep learning technology at present. But the deep learning technology is all for the realization of pixel discrete point, it is difficult to achieve sub-pixel precision. The experimental results showed that the algorithm could meet the actual production requirements, and could achieve real-time and accurate weld extraction.