Abstract: This paper applies the digital image processing to the welding workpiece picture,which is shot by CCD video camera in natural light,and detects the weld seam characteristics.According to the weld seam characteristics,two methods are used to detect the weld seam.One is the detection of median filter-Laplacian image sharpen-Roberts operator-abstracting weld seam,the other is the detection of median filter-self-adapt threshold image segmentation-abstracting weld seam.The comparison of the experiment results shows that the later method is a useful way to recognize the weld seam.