Abstract: Chaotic and stochastic behaviors of natural phenomena are fully diffirent.It is the foundation for simulation and prediction of flood flows to distinguish the behavior of a system which will generate them from their stochastic behavior.This paper deals with the identification of these two behaviors froma time series of flood flows and based on the analysis principle of chaos.The results show that the time series of flood flows at Pinshan station are characteristic of chaotic behavior,that is,a strange attractor may exist.Such a strange attractor has fractal dimension,positive Lypunov exponent and Kolmogorov entropy.Therefore,the complex phenomena of flood flows may result from the evolution of an inherent non-linear dynamic system.