Abstract: To address the conflict between ecological and navigational water demands in the Lijiang River and mitigate water scarcity during dry seasons, this study conducts a detailed analysis of flow evolution characteristics in the river channel. The aim is to facilitate efficient and precise water supplementation from upstream reservoirs. Focusing on the segment from upstream reservoirs to the Guilin hydrological station, the research employs segment-by-segment simulation and time-phased data analysis. Utilizing methods such as data mining, function construction, and curve fitting, the study optimizes the characterization of flow evolution over time across different flow magnitudes in each river segment. The findings reveal that: 1) Linear functions suitably describe flow evolution in upstream mountainous river channels due to their distinct mechanisms, while nonlinear functions are preferable for middle and lower reaches; 2) The developed functions exhibit high calibration accuracy, with relative errors generally below 10% and RMSE typically less than 1.7 h. The analytical outcomes are applied to assess past water supplementation tasks and plan new strategies, demonstrating their efficacy in enhancing reservoir water supplementation efficiency.