Abstract:In order to analyze the changing trend of environmental flow factors in Huaihe River Basin and its ecological impact on fish habitat in Hongze Lake, IHA(indicators of hydrologic alteration)method was used to study the middle and lower reaches of Huaihe River. The runoff series of Bengbu Hydrological Station from 1950 to 2015 was divided into two periods before and after the expansion of Bengbu Gate in 2002.32 environmental flow evaluation indexes were screened out by using five flow events. Taking mandarin fish as indicator fish in Hongze Lake and considering habitat restriction factors comprehensively, the area-flow curve of habitat was obtained by using PHABSIM model, and the ecological flow of mandarin fish during spawning period was calculated. The results show that the composition of environmental discharge in the middle and lower reaches of Huaihe River tends to be simplified. The flood events are reduced, the low water flow is increased, the duration of high pulse flow is shortened and the frequency of occurrence is increased, which is harmful to the ecological environment in the lower reaches of Huaihe River. The minimum ecological flow rate of mandarin in Hongze Lake during spawning period from April to June is 300m3/s, and the suitable ecological flow rate is 550m3/s. In order to maintain the ecological balance of Hongze Lake, it is necessary to regulate environmental flow reasonably, increase fish replenishment and material cycle, and take measures such as lake ecological restoration.