Abstract: Existing physical habitat models could only be available and efficient for the rivers which have abundant monitoring data. To overcome this shortcoming, a new physical habitat simulation method by applying fuzzy logic inference was presented. Based on precise flow field simulation results, the proposed fuzzy habitat model linked these data to the expert knowledge base to compute habitat suitability indexes of each unit by using fuzzy logic reasoning. At last, the weighted usable area and highly suitable proportion of habitat at different river discharges were calculated to study the ecological water requirement. By using the proposed method, Chinese sturgeon spawning habitat on the downstream of the Gezhouba Dam was simulated. The results indicate that the suitable ecological flow range for Chinese sturgeon propagation is about 10 000-17 000 m³/s. The proposed method which is weak dependence on monitoring data by considering expert knowledge and experience is feasible and available. This research could be helpful to ecological protection and river management for the rivers which are lack of field-measured data, and could also provide a reference for the application of fuzzy mathematics in water ecology.