Abstract: Aiming at the problem that conventional MIG welding is difficult to adjust the welding position in real time according to the group deviation and thermal accumulation deformation, a weld seam tracking method based on passive vision is proposed. Through the image spatial domain filtering and automatic enhancement algorithm, the YOLO v7 deep learning model with attention mechanism is used to extract and analyze the groove alignment position and arc position in the region of interest in real time. The fuzzy control algorithm is used to control the MIG welding process in real time when the preset deviation occurs. The results show that, the image automatic enhancement algorithm is used to complete the preprocessing of the image, and the pixel gray value of the edge position is increased from 40 to about 110, which significantly improves the accuracy of the edge position information extraction; Based on the YOLO v7 network structure, the attention mechanism module is added to improve the efficiency of target detection, and the mAP index is as high as 99.27%. The preset deviation test shows that the pixel error of the alignment deviation detection is within 8 pixels, and the alignment deviation distance is controlled between ± 0.5 mm.