The characteristics of the general atmospheric circulation during the catastrophic flood period over Yangtze River Valley in 1998 are discussed. There are two patterns of precipitation distribution: the pattern of floodwater over Yangtze and Precipitation more than normal in the whole country, and the pattern of floodwater over Yangtze and precipitation less than normal in its north and south. The 500hPa circulation characteristics of the two patterns are studied. The results show that there are obvious difference of the 500hPa circulation in the northern hemisphere. The establishment of Okhotsk Sea Blocking High is a major factor in causing the floodwater over Yangtze valley and the intensity of South China Sea High is a important factor of forming the pattern of floodwater over Yangtze and precipitation more than normal in the whole country. [
