s ： By using the image processing and numerical functions of MATLAB, after the treatment of SEM image to mudstone specimen with threshold segmentation, filtering and other procedures, we can obtain binary image of mudstone; and determine the fractal dimension of the image by MATLAB program. The results showed that: MATLAB fractal image processing is simple and convenient, the computation of regular fractal dimension by using Koch curve showed that the calculating results in this way are accurate and reliable. The calculation of the mudstone fractal dimension showed that mudstone has different fractal dimension under different intensities. On the whole, the bigger the intensity, the smaller the fractal dimension.