The cause of storm rainfall and flooding in the Yangtze River Valley was analyzed in this paper. It was closely connected with the anomalies of the Cross-Equatorial Flow-(CEF) and the influence of African-Asia "Large-scale Synoptic Systems between Two Hemisphere". At the same time, it is pointed out that not only the storm rainfall and flood disaster in the Yangtze River Valley could be predicted in time, but also could be controlled and reduced by weather modification.