Based on NCEP/NCAR reanalysis data and rainfall data from 753 weather stations in China,the causes for droughts in the eastern region of the southwest part of China(ESWC) are discussed in this paper.The results indicate that both interdecadal and interannual changes are obvious in the precipitation in ESWC.The main characteristic of interdecadal change was that a sudden shift from wetness to dryness appeared around the late 1980s in ESWC;the interannual variations of precipitation are highly related to the SSTA over the regions from the eastern Indian Ocean(around Sumatra) and western Pacific(EIWP) to eastern Pacific(EP).By inducing abnormal atmospheric heating,the positive and negative abnormal patterns in SST over the EIWP and EP induces cyclonic circulations around South China Sea and Bay of Bengal,together with enhanced Hardly Cell.In this case,the studied area is then controlled by both northerly wind and enhanced downward vertical motion while the water vapor transport from the Bay of Bengal is reduced.All the above reasons lead to droughts in the studied region.The above observational results are further confirmed by a series of numerical model simulations using NCAR CAM3.0(Community Atmosphere Model 3.0).