The climate of Southwest China is wet all year round， but the frequent drought disasters in recent years have caused huge economic losses such as crop yield reduction and forest fire.In order to fully understand the anomalies of water vapor transport in drought years in Southwest China and provide reference for early warning of drought disasters in this area in the future， this study used TRMM and APHRODITE precipitation data to analyze the interannual variation of precipitation and the interannual variation of precipitation in various seasons in Southwest China from 1998 to 2019， selected the summer dry year （2011）， autumn dry year （2009） and 2008， which were relatively wet in summer and autumn.Using Lagrangian transport model FLEXPART， we tracked the paths of water vapor transport and water vapor sources in the two extreme dry seasons （the autumn of 2009 and the summer of 2011）， and compared with the summer and autumn of the wet year （2008）， respectively.The results showed that： （1） The paths of water vapor transport in dry and wet year are consistent， and the paths in southwest China in summer can be divided into three main paths： the southwest path， the southeast path and the northwest path， among which the most dominant is the southwest path， so the main water vapor source area are the Arabian Sea——the Bay of Bengal.In autumn， the main paths can be divided into two： the southeast path and the northwest path， of which the most important is the southeast path， so the main source of water vapor is South China Sea——the Pacific Northwest.（2） There are differences in the strength of water vapor transport between dry and wet years.The reason for the drought in Southwest China in summer is that the water vapor transported by the southwest route is weak， while the reason for the drought in Southwest China in autumn is that the water vapor transported by southeast route is weak.