Abstract: An algorithm of weld seam recognition based on color analyzing is proposed for automatic welding and automatic nondestructive test technologies.Based on color theory and the principles of image segmentation, the image representation in RGB(red, green and blue) color space is studied, and the method of color space transformation is proposed.The experiments demonstrate that the image described in the newly defined color space is able to be segmented by threshold value, which allows the seam region to be located and makes the algorithm and recognition easy.