There is a north-south reverse pattern in precipitation in flood season(May to September) over the Tibetan Plateau.Based on the monthly rainfall data of 67 stations over the plateau from 1967 to 2008,this paper studies the principal spatial patterns of monthly rainfall during the flood season,and the moisture configurations and circulation anomalies in the early summer(May to June) and midsummer(July to August),respectively.It is found that there are two main patterns in summer,but they are different between the early summer and midsummer.The former has an advantage in north-south reverse type(NSRT),while the latter exceeds in whole region consistent type(WRCT).When the rainfall shows NSRT,the moisture transport comes from south to north Tibetan Plateau in the early summer,and the convergence(divergence) of water vapor locates in north(south) Tibetan Plateau in the midsummer.While the rainfall shows WRCT,the moisture transport comes from western Pacific in the early summer.In the midsummer,it comes from the eastward ransport of water vapor from Arabian Sea,which enters the plateau from its southwest areas.At 500 hPa,the meridional(zonal) geopotential height differences between the two patterns are predominant in the early summer(midsummer),and the circulation systems impacting distributions of precipitation anomalies are mostly deep.