Abstract: An extremely great flood occurred over the Yangtze River, Nenjiang-Song huajiang regions, and Pearl River during the summer of 1998, its meteorological and hydrological characteristics and causes are presented. Pearl River, Yangtze River, Nenjiang-Songhuajiang basins had successive heavy rains in the second half of June. Yangtze River valley experienced the second period of the Meiyu in the last ten-day period of July. Heavy rainfalls centered in Zhalantun were observed over Nenjiang-Songhuajiang regions in first half of August. Frequent heavy rainfalls brought about the rapidly rising water level in most part along the middle reaches of Yangtze, Nenjiang, and Pearl River, and led to the greatest floods in the recent 100 years. The southward shifted subtropical high over the West Pacific was responsible for the second period of Meiyu. The right mixture of subtropical high, monsoon swell from South China Sea, cold air mass coming from mid-high latitudes, and MCSs from the Tibetan Plateau contributed to successive heavy rains over the Yangtze River valley.