Seam tracking technology is an important research area in automatic arc welding, precise seam tracking has a very important role to improve the welding quality.In order to achieve precise seam tracking,the weld deviation (the deviation between the center of the weld and arc) detection technology is a key.Through image processing technology, the pool area of image processing(including the front of molten and the front end part of the weld) was selected, and weld pool centroid was taken as the characteristics of the weld deviation, to study the method of creating the welds deviation measuring visual model using the characteristic parameters of the weld pool.