Abstract: Based on the daily meteorological data from 5 national meteorological stations in Kaidu River Basin from 1961 to 2020,the standardized precipitation evapotranspiration indexes（SPEI） on annual and seasonal time scales were calculated.Morlet wavelet analysis,Mann-Kendall test,Trend attribution and other methods were used to analyze the spatial-temporal evolution rules of drought and its reasons in this basin.The results showed that the basin presented an aridity trend during the past 60years except for winter.Spatially,from north to south in basin,the distribution characteristic was“wetry”trend both year and summer.From west to east in spring and autumn,there was a“dry-wet”trend.The overall trend in winter was“wet”.Temperature was the dominant factors of the dryness changes in the Basin.However,the drought change in the north region and the south region were affected by precipitation and temperature respectively.Except the winter,the contribution of temperature to the dryness trend in Hejing region and Yanqi region exceeded that of precipitation,which indicated that these regions were severely arid.The different time scales drought occurred every 2 to 6 years in basin,which were mainly light drought or moderate drought.Besides,spring was not only the event-prone period with the serious drought,but also the main periods for drought events occurred.