Abstract: On the base of the fractal model for bentonite surface, Xu et al.1 proposed a new method to calculate the swelling deformation of bentonite and expressed as the equation Vw/Vm=KpDs-3(Eq.(1)),which were verified by the experimental data of swelling deformation and swelling pressure of Tsukinuno bentonite, Wyoming bentonite and MX-80 bentonite. Due to the limitation of experiments, two factors to be improved are listed as follows：(1)the fractal dimension obtained from the swelling test was not validated with results of the N2 isotherm adsorption; (2)the expression of the parameter K in Eq.(1)was given on the basis of an empirical equation. In this paper, the surface fractal dimension of Gaomiaozi Na-bentonite and Ca-bentonite, a commercial bentonite and Tsukinuno bentonite are measured using the N2 isotherm adsorption. The swelling deformation is calculated and verified from the above equation using the surface fractal dimension of Gaomiaozi Na-bentonite and Ca-bentonite, a commercial bentonite and Tsukinuno bentonite. Expression of the parameter K in the above equation is deduced from the diffused double layer(DDL)theory.