Abstract: In this paper, the fractal characteristics of fissure structure in expansion soil are studied based on fractal theory. The mechanical effect of fractal dimensions of fissure network and fissure surface in expansion soil is analyzed. The results show that fissure network and fissure surface of expansion soil have a high self similarity in statistics .Fractal dimension can describe quantitatively the mechanical effect of fissure structure of expansion soil, and it has a close relationship between fractal dimensions and indexes of shear strength of expansion soil. At last, the significance of research is discussed.