Dongting Lake takes on the functions of regulating, diverting and storing excess flood and is the vital area for the Yangtze River flood control construction. At present, there are lots of studies on the flood routing in middle reach of the Yangtze River. Although it is also included in them, no attention is paid to flood routing in Dongting Lake to analyse its the complexity. The flood characteristic was analyzed based on the Dongting Lakes flood event in 1998, using coupling hydrodynamic model with 1-D and 2-D for Dongting Lake area. Both the characteristic of water surface and flow fields show the changes of Dongting Lake from river-like at low water elevation to lake-like at high. The obvious differences in hydrology and hydraulics between both the east and south two lake areas and the west lake area are presented.