Abstract: In recent years,China has increased funds for dam rehabilitation,and a large number of dangerous reservoirs have been modified in a short time.It results in the general improvement of dam safety in China.However,some dam failures happened during the implementation of reinforcement projects or after the modification,indicating that some important elements could not be ignored for the reinforcement of dangerous reservoirs.Based on the investigation and analysis of four dam-break cases of dam reinforcement projects,the failure reasons were sought from the aspects of the dam safety appraisal,the review of appraisal results,the preliminary design and review of the reinforcement projects,the construction quality control,check and acceptance,as well as the operation and management,etc.Recommendations and countermeasures for the improvement of dam reinforcement projects are put forward in administrative,technical and cognitional aspects.