Abstract: By the use of summer precipitation data of 81 stations,NCEP/NCAR monthly data reanalysis and SST data provided by Hadley Centre,we have introduced a new approach to constructing drought index based on the Generalized Extreme Value (GEV) distribution.Meanwhile the circulation background of summer drought in Guizhou has been analyzed.The results show that the precipitation in Guizhou parallels Weibull distribution pattern,and distribution scale parameters show that the summer precipitation south and northeast Guizhou has great interannual variability.Summer drought index of Guizhou witnesses obvious interannual variations,and can monitor the distribution of drought to a certain extent.The summer drought index of Generalized Extreme Value (GEV) in Guizhou can help us to analyze the summer drought anomalous cyclonic circulation formation.The lower troposphere in the Indo China Peninsula and the South China Sea and the Pacific Northwest,over the Southern Ocean anomalies over the anticyclonic circulation can reduce water vapor transport in the area of the bay of Bengal and India ocean,and result in water vapor flux divergence in Guizhou,which is not conducive to the formation of the local precipitation.At the same time,the abnormal vertical circulation in Guizhou is significant in sinking motion control,whether it is from the South warm moist air flow or northern cold air is often an average somewhat weak,leading to drought.Finally,the drought index in the same period in the northern Indian Ocean and Northwest Pacific SST presents close relationship.The anomaly SST in the northwest Pacific and Indian Ocean can be used as an early signal to predict summer drought of Guizhou region.