The analysis for the highest water level,flow quantity of peak flood and flooding disaster\|caused area at Chenlingji Hydrometric Station of Dongting Lake in the years of 1950 to 1999 has shown that disastrous flood of Dongting Lake concurred in high frequency and with huge energy dissemination and strong capacity of sand transportation and that the floods are direct and/or ind.

The loses caused by disastrous flood is far too serious in Changsha city where is among the important cities of flood prevention in China.

Thus the method is proposed as a possible approach to long-term forecast for disastrous floods.

Fuzzy method is significance for us to evaluate of vulnerability of disaster bearers because rainfall and density of population is fuzzy in forming vulnerability to flood.