Abstract: In this paper, the drought or flood early summer over South China is defined based on monthly rainfall of May, 1961-1980. The relationship among those two extreme periods and the structure of monsoon circulation is analysed from the viewpoint of synoptic climatology by seclecting 1963, 1966 (drought), 1973, 1975 (flood) as examples. The main results are as follows:1.The differences in the time of onset, maintenance, and strength of summer monsoon are obvious during drought or flood May over South China;2.There is also obvious contrariety in the global circulation, especially of the active centres in high and middle latitudes prior to drought or flood may over South China, of which the differences are more attractive on Aleutian low and Iceland low in January and on Pacific high and Atlantic high in April;3.The rainfall of May over South China is closely associated with the low lititude pressure index in March, when the pressure index is above the normal, the rainfall usually is more, when the pressure index is below the normal the rainfall is less.