The causes of summer flood/drought extremes in Chongqing were analyzed based on the data during 1961-2010recorded by 34meterorological stations in Chongqing,NCEP/NCAR reanalysis data and the characteristics of circulation over China provided by NCC (National Climate Center in Beijing). The results indicated that the summer flood/drought extreme events in Chongqing were characterized by an obvious inter-annual variation.Overall,Chongqing was liable to drought in the 1960s and the 1970s but to flood in the early 1980s.Greater fluctuations occurred in the late 1980s,with alternate drought and flooding.When the Western Pacific Subtropical High(WPSH)and the ridge line of the South Asia High shifted northward (southward),drought(flood)was likely to occur in Chongqing.The flood/ drought also depended on the strength of water vapor transport,the water vapor convergence upward movement and the influence of activities of northern cold air.