Leiocassis longirostris (Chinese Longsnout Catfish) is classified by IUCN as data deficient, but population declines have been reported in China. Protection of the migration and overwintering habitats of L. longirostris was selected as the key environmental flow objectives for the main stream channel of the Huai River. First a conceptual model of the relationship between the ecological requirements of L. longirostris and the flow regime was established. Then the FLOWS method was extended by modelling the change in preferred physical habitat over time. Finally flow components suitable for survival and reproduction of this species were defined. Results of the analysis of environmental flows showed that high flow pulse occurred more frequently and with longer duration prior before the hydrological change, while the frequency of flooding increased after the change, so the environmental flows before change was more suitable for L. longirostris. Results of the analysis of satisfied degree of the assumed critical hydraulic parameters showed that the flow regime in the period prior to the hydrological change was more suitable for L. longirostris. So the mean water year before the change (1970 Year) was selected to characterize suitable environmental flow components. The suitable flow range for the spawning period was 545~1212 m3/s, the minimum flow for larvae feeding period was 1750 m3/s, and the minimum flow over the overwintering period was 74 m3/s. These research findings can assist in the protection of rare species and maintenance of ecosystem integrity in the Huai River.