Abstract: The characteristics of 20th drought in Southwest China at different time scales have been investigated based on SPEI (Standardized Precipitation Evaportranspiration Index), which is a multi-timescale drought index and takes temperature into account. Firstly, in comparison with observations, the SPEI is confirmed to be applicable to analyze the drought in Southwest China. Secondly, the results present that at longer time scales the SPEI have a feature of interdecadal variability with minimum values of SPEI appearing around 1940 and in August, 2006. In contrast, the temporal evolutions at shorter time scales of the SPEI are characterized by seasonal to interannual oscillations. Sometimes, the droughts at different time scales may happen simultaneously, which may produce extreme drought events affecting society and economy seriously (for instance, the summer drought in 2006 in Sichuan and Chongqing). However, compared with the summer drought in 2006, the summer drought in 1972 is not that severe because there is no overlap of droughts at different time scales. Finally, the contribution of temperature anomaly to the drought is also analyzed. The result indicates that high temperature contribution cannot be neglected and its probability can reach as high as 20%-25%.