We investigated the abrupt alternation from flood to drought in southern China during summer 2019 using mul-tiple datasets.Positive anomalies of precipitation occurred in southern China in the summer of 2019 and the daily precipitation in the south of the middle and lower reaches of the Yangtze River valley showed an abrupt change from flood to drought conditions around mid-July.The highest precipitation in 39 yr was recorded between 1 June and 14 July 2019.The circulation systems affecting this high precipitation included a persistent deepened East Asian trough,the southward location of the western Pacific subtropical high,an intensified East Asian subtropical jet,an anomal-ous low-level cyclone from southern Japan to southern China,and extremely strong positive vorticity over the Jiang-nan area.Completely different atmospheric circulation anomalies from 15 July to 31 August caused continuously high temperatures,below-normal precipitation,and severe drought in Jiangnan area.Further investigations showed that the sudden change in atmospheric circulation around mid-July started in the mid and lower troposphere and was influenced by the northward track of Tropical Cyclone Danas in the northwestern Pacific.