Abstract: Weld edge is the most important characteristic in a weld image.The fact of selecting an appropriate edge-detecting operator and obtaining the accurate weld edge information is a key process in weld image processing.The canny operator was used to extract the weld edge,and its principle and implementation were discussed.And the canny operator,kirsch operator,prewitt operator,robert operator,sobel operator and gauss-laplace operator were applied in detecting the weld edges to test the effects,respedively.The analyzsis of the weld image and weld center coordinates showed that the canny operator is a very effective way to detect the weld edge,and also suitable for the seamtracking process based on vision sensors.