Analysis of the structure of most irregular porous materials has recently been developed on the basis of the concepts of fractal geometry. The geometry enables general statements about so-called irregular structures to be made in terms of a few well-defined mathematical ideas, e.g. self-similarity and scaling, and a few mathematical parameters, e. g. fractal dimension. Gas adsorption is an ideal tool for characterization of the pore structure of xerogels and other porous materials. In this short paper, a simple and effective method to determine the fractal dimension of xerogels is presented. Instead of carrying out a series of gas adsorption/desorption experiments with various gases, only one gas adsorption/desorption experiment using a kind of gas is needed here. By studying the relations between the scaling and the data of pore size distribution and specific surface area, both surface fractal dimension and pore distribution fractal dimension can be easily derived. The reliability of the results is realized by performing error analysis and correction. The effectivity of the method is tested by experimental N2 adsorption/desorption data of silica xerogels prepared with sol-gel routine.