Flood disaster has seriously influenced people's safety of lives and property in the lower reaches of Weihe River. The purpose of this article is to analyze the causes of the disaster and its prevention. The main causes are found through contrasting and analy zing flood amount and level in history, such as deforestation for farming in the upper reaches and building of embankments in the lower reaches which affects the stability of river conditions and impede the smooth passage of floodwater. Due to Sanmenx ia Reserv oirs operation, heavy silting raises the riverbed in the main channel and makes flood disaster easily happen. To handle this problem, firstly we should have the right thoughts and make the breakthrough and innovation on the way and prevention. We should mainly take dredging, combine dredging and blocking tog ether, and lower river bed to solve the problem. In addition, we should reinforce river bank, combine engineering with biological practices, make scientific water and sediment transportation, and return the field to river. All of these should be done to guarantee the safety of Weihe River.