In this paper, a 3D composite seam image has been firstly preprocessed and then the centerline and key-points have been extracted. After that, a method has been proposed which is based on the optical deviation detection-lateral and vertical deviation detection of the seam. Seam simulation is immediately carried out with MATLAB. It turns out that the deviation error is less than 0.004 mm, and that stitching simulation route are basically the same as the actual seam. It also demonstrates that this method is practical and effective.