The mechanism of the flood disasters is analyzed based on the understanding of the flood history in the Hongze Lake..It is considered the the natural factors and human actions lead to the floods in the Hongzehu Lake Basin.Typical vulnerable geographic transition location is the basic environment background of floods,heavily intensified precipitation trigger floods in the lake drainage,historically induced high altitude and the inverse vertical section ratio are the fundamental reason,and the low flood discharge standard combined with the human influence also plays an important part in the flood disasters.The above- mentioned mechanisms can be taken as a scientific guide for the prevention of flood disasters in the Hongzehu Lake Basin and the middle reach of the Huaihe River.