Abstract: In this paper,The characteristics of flood events series have been analyzed by using fractal theory,it is shown that the flood events have the character of self-similarity,and is a fractal.Further,a case study on the seasonal flood periods classification at the station of Xiao Deshi in Ya Long river is given,the results show that the periods determined by using fractal theory are consistent with that from traditional method.In comparison with traditional method,the new method is much more objective.