Abstract: The invention relates to a machine vision seam tracking method and apparatus for welding robots, particularly to an apparatus which can automatically detect the deviation between an actual welding seam and a taught path where the apparatus so as to correct the welding path, comprises an image forming means and an image processor. Through the image forming means, a light coming from a common light source, after being condensed and transmitted, can be projected onto a workpiece to form a line of light across the welding seam. A solid state camera disposed along the direction of the welding seam can detect the image of the welding seam which in turn is transmitted to the image processor.