By using the NCEP data of the first 10 days in July from 1998 to 2007, three hea vy flooding cases in 2003, 2005 and 2007 are analyzed and compared. It is foun d that there is an obvious difference in the atmospheric circulation background , the high/low level jets and the water vapor transportation between the floodin g years and average of ten years. The abnormal feature of the East Asian summer monsoon is the main reason of the floods. During the first 10 days in July of t he three flooding years, the west pacific subtropical high is stronger and its west ridge point is more western than the tenyear average. There is obviously north wind from the south of northChina to the Huanghe and Huaihe basin. The low jets of 850hP a surpassed 6m/s larger than the tenyear mean. The connection of the north and the south strong air current exactly lied in Huaihe River basin. At 200hPa, Hua ihe River basin was under the south of the jets entrance or under the anticyclon e. Through the analysis of abnormal water vapor transportation on the whole laye r, it is found that the South China Sea was the main water vapor source area.