Abstract: Serious flood occurred in the extremely-heavy Meiyu episode over the Yangtze and Huaihe Valleies in 1931.The disasters and death toll were the highest of Meiyus in recent 121 years(1885-2005).The characteristics of precipitation,the abnormal changes and the influence factors of atmosphere and ocean are studied.Some of the important influence-factors can be seen in the winter of last year or about 2-6 months before the extremely heavy Meiyu in 1931.So that these factors can be considered to be used for the long-range weather predictions.