Abstract: In this paper, the structure of the mean meridional circulation and its evolving features over East Asia before, during and after the Mei-yu season for the Changjiang and Huaihe River Basin in 1983, are studied. For different periods, the circulation of the Indian tropical monsoon and the East Asia tropical and subtropical monsoon differ significantly. The research shows that the Mei-yu for the basin results from the interactions among the 3 summer monsoon systems in Asia. Its onset is a consequence of the ascending branch of the meridional circulation in the East Asia subtropical monsoon system, closely related with 2 other monsoon systems. Its ending has something to do with the southward withdrawal of the weakened Indian tropical monsoon circulation, the westward extension of the increased West Pacific High, and the northward advancement of the East Asia subtropical monsoon circulation.