Abstract: Although the reservoir projects at home and abroad have played a tremendous role in flood control,irrigation,power generation,water supply,shipping and aquaculture,because of the life span of dam,functional degradation,and higher maintenance costs of the reinforcement,some of the reservoir dams will be removed or retired.A way of understanding potential impacts induced by the removal of dams is to recall the results of the construction of the dams in the river system.Firstly,dam construction and its environmental impact are reviewed from the impacts of climate,water quality,biology and reservoir sedimentation caused by reservoirs.Based on domestic and international practices,the status of the removal of dams in China and the United States is reviewed,and the reasons for dam removal and space-time impact of the ecological environment due to the dam removal are analyzed,and the methods for evaluating the impact of the ecological environment are summarized.The investigation of a reservoir was done for the first time in China.The results show that construction and removal of dams are complicated,and that the studies on the ecological environment impact due to decommissioning and removal of dams are of great significance.