Using the daily precipitation observation data of 121 stations in the southwest China from 1961 to 2019， the southwest China is divided into three regions： southwest I， southwest II， and southwest III， according to the REOF positive anomalies of precipitation， and analyzes the characteristics of abrupt drought-flood alternations of these districts.The results show that there are obvious regional differences and similarities in the abrupt drought-flood alternations in summer in Southwest China.There are fewer severe abrupt drought-flood alternations in region I and some strong abrupt drought-flood alternations mainly occurred before 2000.And there was a relatively obvious interdecadal oscillation in the abrupt drought-flood alternations index in region II from 1961 to 1990， more drought-to-flood events occurred from 1961 to 1970.What’s more， there are more flood-to-drought events occurred from 1971 to 1980.Then the intensity of abrupt drought-flood alternations from 1980 to 1990 was more pronounced.Smaller， it gradually turned into an interannual oscillation after 1990.The overall abrupt drought-flood alternations index in region III was relatively low.It has obvious interannual oscillations from 1975 to 2000.But after 2010， the abrupt drought-flood alternations events showed an increasing trend.Further research on the atmospheric circulation characteristics of typical abrupt drought-flood alternations years in each region found that during the drought period of the three regions， at mid-to-high latitudes， high-altitude westerly winds were strong and zonal air currents prevailed.At mid-low latitudes， the western Pacific subtropical high was stronger to the west， the South China Sea-Pacific and Indian Ocean-Bay of Bengal water vapor transport was weak， and sinking air currents prevail in the lower layers， resulting in less precipitation.The circulation situation during the flooding period in the three regions is complex.During the flooding period in region I， the mid-high latitude circulation presented a "-+-" zonal wave train， the Ural Mountains high pressure ridge deepened， the western Pacific subtropical high was northeast and east， the water vapor transport in the Bay of Bengal was enhanced， the upward movement was enhanced， and the precipitation was more frequent.While during the flooding period in region II， the mid-high latitude circulation presented a "-+" zonal wave train， the Okhotsk high pressure ridge strengthened， the western Pacific subtropical high was northeast and the southern branch trough was obvious， and the water vapor transport in the Pacific and Indian Oceans enhanced.So that the precipitation is on the high side.However， during the flooding period in region III， the mid-high latitude circulation presented a "+-+-" zonal wave train， the Ural high pressure ridge and the Baikal low pressure trough strengthened， the western Pacific subtropical high was northeast and the Gulf of Bengal-Indian Ocean water vapor strengthened， and precipitation was more frequent.