The heavy storm rain from May 21 to July 13,1991 caused huge torrents and hit this area. About 3309km² in Taihu Plain were submerged by the flood water with total economic losses of US $ 2×10⁹.According to the investigation and statistics it is showed that about 45.0% of the area was below 4.5m and 52.2% of the area below 3.5m,but the water stage during the flood time reached 4.79m,so that about 62.5% of the area below 4.5m was inundated by the flood water. About 95% of the flooded area belongs to the paddy field and vegetable land. About 4 million people were affected by the calamities.On the basis of distribution of the flooded area,it can be divided into fiv