Abstract: An investigation of the effects of annual runoff wet-dry classification methods is of important significance for hydrological analysis and water resources management in a river basin. Three corresponding indexes,i.e. similarity index,difference index and uniformity index,are defined for evaluating the wet-dry classification effects from the view of annual runoff process similarity,volume difference and distribution uniformity of wet-dry categories. According to the adopted classification index types,annual runoff wet-dry classification methods are divided into three categories,i.e. comprehensive index-based（CI-based）category,relationship index-based（RI-based）category and comprehensive relationship index-based（CRI-based）category. Moreover,nine representative methods are selected from the three categories,and each category contains three methods. Finally,Yingluoxia Station of Heihe River Basin is taken as a case study,where the selected nine methods are applied to the annual runoff wet-dry classification of the station,and the wet-dry classification effects of different methods are analyzed. The results show that（1） annual runoff wet-dry classification results are very sensitive to classification methods and their internal parameters,classification results of different methods are obviously different,and the classification effects of the same method may also differ from region to region；（2） the three defined indexes may reflect the wet-dry classification effects of different methods,and the uniform distribution of wet-dry classes is beneficial for the improvement of wet-dry classification effects；（3） overall,the classification effects of the methods of CRI-based category are the best,those of CI-based category are the second,and those of RI-based category are the worst;and（4） the classification results of conventional methods may be more reasonable than those of comprehensive methods when the annual runoff volume and process are relatively consistent. The results can provide a scientific basis for reasonably classifying annual runoff wet-dry states of a river basin.