Abstract: Based on gray space and C-Canny operator, an edge detection algorithm of color image is proposed. And the Canny operator has been improved, using 3 × 3 neighborhood to calculate the gradient magnitude. The improved Canny operator gets a good effect on the noise suppression, and the detected edges are much more refined. Two transformation algorithms of color image to gray image are used. Execute C-Canny operator on the transformed image, and the result will help us complete edge detection on the color image. Based on our algorithm, the experiment showed that we will get good continuity and high veracity of image edge, and better edge detection will obtained on the color image of small number of colors.