The color of tongue coating is an important feature in tongue diagnosis of traditional Chinese Medicine. In order to solve the problem of color distortion in image acquisition of TCM tongue image in natural environment, when shooting the tongue image, the standard color card is placed beside the tongue to shoot together, and the polynomial regression algorithm is used to correct the color of the image. Experimental results show that the proposed method is more accurate than perfect reflection algorithm, gray world algorithm, color deviation detection and color correction algorithm.