From 15 to 20 July, 2004, there was a continuous storm on the upper reaches of the Dayingjiang River and Ruilijiang River in the Irrawaddy River Basin. The largest 3-day rainfall is 428.3 mm. This heavy storm led to a suddenly rising of the water levels in the rivers of Dayingjiang and Longchuanjiang, and caused such flood damages as landslides, mud-rock flows, mountain torrents and etc. in the areas of Zhina, Zhanxi, Mangzhang in Dehong Prefecture. Analysis of the cause and characteristics of this storm flood will contribute to understanding the formation conditions and changing law of the storm floods in this watershed, so as to provide basis for flood control and disaster reduce.