To study the impacts of dam removal on river ecosystems, the response of key ecological components, such as river hydrological conditions, topography, riparian plants, fish, and zoobenthos, to dam removal are analyzed from both the short-term and long-term perspectives. Two currently used major assessment methods are summarized, including assessment of actual removal conditions and numerical modeling forecasting. Field surveying is considered the most direct and convincing research tool, but it is limited by cost and other uncontrollable factors. Numerical simulation has remarkable advantages, such as high speed, low cost, and freedom from scale effects, and can forecast the influence of dam removal and provide decision references for managers. However, the precision and accuracy of simulation need to be improved. It is pointed out that further studies should comprehensively consider the coupling effects among various ecological factors in the process of dam demolition, and the impacts of different demolition times and dam removal phases on river ecosystems require deeper examination in the future.