A method on the feature extraction of coal and rock character recognition was mainly put forward based on image gray level distribution and gray scale average value. In order to improve the recognition effects of the image, cropping, gray level transformation, contrast enhancement, median filtering and other preprocessing work were applied individually on the raw image of coal caving and rock caving acquired from mechanized top caving face, then gray histogram of image signal of coal and rock was abstracted and the gray scale mean were calculated. The results shows that (1) the range of gray scale of top coal caving image is mainly between 10-100, and the range of gray scale of top rock caving image mainly between 90-220, (2) the gray scale mean of top rock caving image is around 130, far higher than the gray scale mean of top coal caving image of 66.