Abstract: Changes in hydrological conditions are the main factor in the function of river ecosystems. In view of the changes in the hydrological situation of the Minjiang River Basin caused by the construction and operation of water conservancy projects,the representative hydrological station,Gaochang Station at the intersection of the Minjiang Tributary Dadu River and the mainstream downstream of the Minjiang River is selected for 62 years（1956-2017）daily flow data by using the Mann-Kendall Method,Cumulative Anomaly Method,mean difference T test method,and sliding T test method to analyze flow characteristics,and consider the hydrological project construction to split the hydrological indicators before and after a sudden change,and select the ecological hydrological indicator change range method（IHA-RVA）and hydrological change degree method to comprehensively evaluate the changes in the hydrological regime of the Minjiang River,and qualitatively analyze its impact on fish in the lower reaches of the Minjiang River. The results show that from 1956 to 2017,the average annual flow of the Gaochang Hydrological Station in the Minjiang River Basin showed a downward trend;the mutation year occurred in 1993. Through the analysis of the ecological and hydrological indicators before and after the sudden change in hydrological situations,the overall hydrological change in the Minjiang River Basin is 45%. As for moderate change,the change degree of the hydrological index,the rate of decline reached100%;the qualitative analysis of the changes in fish composition before and after the mutation shows that the types and quantities of fish resources have declined to a certain extent,which proves the series operation mode of reservoirs in the Minjiang River Basin and have a greater impact on fish diversity. This study can provide a reference for the ecological restoration and sustainable development of the Minjiang River Basin.