Abstract: Based on the water quality survey of the Erhai basin in 2009,covering 62 sampling points,cluster analysis was done of the data for characterization of the spatial and temporal variation of water quality of the Erhai basin.Spatially,the sampling points were divided into 4 groups,that are,Group A₁,source streams in the interference-free Cangshan forest;Group A₂,upper and middle reaches of the streams and lakes in the farming areas and towns that are subjected to some extent of human interference;Group A₃,lower reaches of the streams running through the farming areas and towns that are subjected to severe human interference;and Group A₄,offshore of the Erhai Lake theat is most seriously interfered by mankind.Discriminatory analysis(DA)was used to identify significant indexes,and to reflect results of the spatial cluster analysis,and the results of the analysisi show that the clustering reached 95.2% in accuracy.By means of principal component analysis(PCA),four groups of principal components were idedntified.Principal Component Group 1 included alkalinity,Ca²⁺,Mg²⁺ and hardness;Group 2,TP;Group 3,TN and NO₃^--N;and Group 4,DOC and TOC.Spatial differences were significant between these groups.On a time scale,Alk was higher in the wet season than in the dry season and Ca²⁺ the other way round.TP did not vary much,while TN in Group A₁ and Group A₃ was higher in the wet season than in the dry season.