This paper gives out an analysis and study on the definition, standards, hydrological characteris-tics and inflow calculation of the synchronized floods in the upper and middle reaches of the Yangtze River. thechange regularity of the storage curves, and the calculation of runoff in the intervening areas in the Dongting LakeRegion. Meanwhile, the forecasting method of the water levels process of 1-5 days lead time at Luoshan Stationunder the condition of svnchronized floods is discussed and the statistics of the forecasting errors is done in thispaper.