It is an inevitable trend that the decommissioned dam will be demolished as the degraded and abandoned reservoirs increased year by year. Considering the removal problem of the retired dam, starting from the number of the dam to dismantle in various countries , dam region distribution, the reasons for dam removal and the relevant policies,, the current situation of dam demolition at home and abroad is analyzed and summarized, and the the impact on ecological environment and social economy after dam removal is summarized .It is found that there is a lack of quantitative analysis and a feasible calculation method.Moreover, it is a single factor study, lacking comprehensive impact factor assessment and analysis. Therefore, it is expected that the future research on the impact of dam removal should be changed from qualitative analysis to quantitative analysis, and coupled with various factors such as hydrodynamics, sediment, biological response and aquatic environment, a comprehensive evaluation system for the impact of dam removal will be constructed.