Abstract: SEM has been widely used to study the microstructure of clayey soil.Other than quantitative methods,most of them were qualitative methods.A method was presented to determine a fractal dimension associated with microstructure of clayey soil by image-processing techniques and Geographical Information System(GIS) software.Through the method of volume-area,the 3D fractal dimension was computed by use of GIS.This method could simplify the data process and raise the working efficiency.Through comparison between area-volume method and perimeter-area method,it was considered that the former method could reflect the 3D information more than the latter one.