Abstract: Whether hydrologic processes are low dimensional chaotic processes is still controversial.After analyzing the litera ture about the research of chaos,we find that there are many problems.For instance,the estimation of the time delay is very subjective and application dependent;in estimation of correlation dimension,many researchers ignore intentionally or carelessly a principle,i. e,there must be a clearly scaling region used for confirming the existence of finite correlation dimension; many researchers still use the original formula of G-P algorithm to calculate the correlation of hydrological time series instead of using the modified formula proposed by Theiler.Therefore,the temporally correlated points in the state space are probably mistaken for a spatial geometry in the state space,and the problem still commonly exits that the size of the studied series by researchers in China is too small.