This paper presents an improved Canny algorithm for locating the edges of cupping spots with an aim toward solving the problem that these edges cannot be completely detected due to the presence of pores, texture, and other impurities on the skin surface. First, hybrid filtering, the four-direction Sobel operator, and the maximum inter-class variance (Otsu) algorithm are introduced to improve the original Canny algorithm, enhancing its adaptability and accuracy in edge localization. Second, the binary image in the CIE L^∗a^∗b^∗ color space is used as a mask area to fuse with the obtained edge image. Finally, the edge images of the fused image and the channel a* image are merged to yield the final detection image. The experimental results demonstrate that compared to the traditional Canny algorithm, the improved algorithm can clearly detect the edge of cupping spots from cupping therapy in traditional Chinese medicine, fully demonstrating the feasibility and effectiveness of the algorithm.