Abstract: In the welding process,the method of image processing has been getting more and more important,especially in tracking control and quality molding.The mathematical morphology is used to analyze the MAG(metal active-gas) welding images.In addition to using the four fundamental gray-scale morphological operations,we especially design a set of the gray-scale morphological algorithms from the image preprocessing to the edge detection on the MAG welding image.The experiment results illustrated that the chosen algorithms were very suitable to the image processing of the welding molten pool.