Numerous debris flows were triggered by the Wenchuan earthquake，bringing a large number of casualties and property loss to the mountain area． For better understanding and prediction of debris flow，particle size analyses were carried out on field samples of debris flow deposits． Fractal structures of debris flow deposits were also analyzed based on fractal theory in the area． The fractal dimension ranged from 2 to 3，with an average of 2．49 and standard deviation of 0． 19，showing a low dispersion degree of fractal dimension． The influences of lithology，total volume of loose materials，and slopes on the particle composition of debris flow deposits were studied． The results show that the deposits of siltstone have the minimum fractal dimension value，followed by those of sandstone and marl． In contrast，the deposits of quartz diorite and limestone have the highest and the second highest fractal dimension value． The fractal dimension values of the deposits increases with the total volume of loose materials，as well as the gully slope． The fractal characteristics of the deposit indicate the risk of debris flow，providing evidences for characterization and prediction of debris flow activities．