An investigation and a sampling determination are made to Gehu Lake, East Tai Lake and Changdang Lake in South Jiangsu after flood. An analysis is made on to the effects of the lake water quality and ecological Environment caused after flood. The conclusion shows that flood results in the suspended matter increasing rapidly, the transparency droppings distinctly, the phytophagous increasing sharply, the water plants reducing evidently, and TN.TP.CODMn rising sharply, then the total Lake water quality is decreasing. On the basis of this result, the suggestions of preventing and fighting flood are raised in this paper.