Taking the Nianchu River, Duoxiong Zangbo and Xiang River in Shigatse City as the research objects, a riverbiologysociety coupling framework was constructed to determine thresholds of suitable ecological flow of the rivers. The water ecological deviation index was used to evaluate the river ecological flow results calculated by different hydrological methods, and the frequency curve method was improved based on the river health index. Finally, the ecological flow calculation results for maintaining the health of the river ecosystem in Shigatse City were obtained. The results show that the minimum values of appropriate ecological flow in the dry season are 3.06 m3/s, 12.91 m3/s and 1.16 m3/s respectively. Among them, to ensure the reproduction and spawning of fish schools in the Xiang River from April to May, the minimum ecological flow needs to be increased to 1.25 m3/s. During the flood season, to ensure the normal operation of the river sediment transport process, the water demand thresholds are determined as 150~180 million m3, 430~540 million m3 and 50~60 million m3 respectively. The analysis shows that the ecological flow deviation indices of the Nianchu River, Duoxiong Zangbo and Xiang River based on the frequency curve method are 0.76, 1.27 and 0.11 respectively, indicating that the calculation results of this method have a high degree of consistency with the local ecological environment characteristics. By adjusting the monthly ecological flow results obtained by the frequency curve method, the improved frequency curve method can make the monthly river health index reach more than 0.4, which meets the local river ecological flow requirements.