Abstract: Based on the precipitation and temperature data of 753 observation stations in China for the period 1961-2012, as well as National Centers for Environmental Prediction/National Center for Atmospheric Research(NCAR) reanalysis and National Oceanic and Atmospheric Administration Extended Reconstructed Sea Surface Temperature v3b data, this study uses the Standardized Precipitation Evapotranspiration Index(SPEI) to discuss the decadal shift of autumn drought in Southwest China and its possible causes through observational analysis and NCAR Community Atmosphere Model, version 5.1(CAM5.1) numerical simulations.The observational results show that the main distribution for the entire district of autumn drought in Southwest China is in the same phase, and the drought has been getting worse since 1994.It is also found that when the western Pacific subtropical high is positioned further west, and is larger and stronger than usual, it is drier in Southwest China.A weak Indo-Burmese trough and local vertical subsidence movement are also key atmospheric circulation factors for autumn drought in Southwest China.The autumn drought in Southwest China is significantly correlated with the sea surface temperature anomaly(SSTA) over the eastern Indian Ocean and western Pacific(EIWP) region, which is the key region for the cause of Southwest China experiencing more drought since 1994.The positive SSTA in this key region enhances the 500 hPa geopotential height over Southwest China in autumn.It also induces cyclonic circulation around the western Pacific, and an enhanced Hadley cell.In such cases, Southwest China is controlled by both northerly wind and subsidence motion, reducing the amount of water vapor transported to Southwest China.A series of numerical simulations using NCAR CAM5.1 confirm the above observational results and show that the autumn positive SSTA in the EIWP region plays an important role in causing the autumn drought in Southwest China on the decadal scale.