Abstract: The distribution of vertically integrated water vapour transportation and flux divergence in the Mei-yu season over the Changjiang River and the Huaihe River basins is studied. The water vapor budget over the Nanhai Sea and the eastern China area is calculated. The results indicate that water vapour associated with precipitation over south China before the Mei-yu period comes mainly from the two air currents which are the Indian southwestern monsoon and the eastern Asian southeastern monsoon, respectively; water vapour of precipitation in the Mei-yu period comes mainly from the Indian southwestern monsoon current; and after the Mei-yu period, the rainy season over North China is mainly affected by the convergence currents from the middle and the low latitude. The analysis shows the Mei-yu period is beginning when the Indian southwestern monsoon current strengthens and moves eastward then northward, and the western Pacific high shifts eastward; and the Mei-yu period is ending when the southwestern monsoon current weakens and declines westward, and the western Pacific high stretches westward and moves northward. In addition, the relationships between the water vapour flux convergence and cloudiness/precipitation over the eastern China are discussed