Abstract: The development and utilization of water resources in the Luolou River basin, a primary tributary of the Jinsha River, are relatively high, leading to socioeconomic water use encroaching upon ecological flow to a certain extent. Influenced by historical dam construction for water diversion, the river channel has long been in a diverted state, resulting in a low level of guaranteed ecological flow in recent years, especially during dry seasons and peak agricultural irrigation periods. Based on runoff and water withdrawal data from the Luolou River basin from 1967 to 2023, this study analyzes ecological flow targets and their historical assurance levels under diversion impacts using multiple methods, including the Tennant method, frequency curve method, Q_p method, and the driest monthly flow method of the recent decade. The research finds that traditional methods are not ideally adaptable for this basin. Subsequently, a comprehensive trial-and-calibration method suitable for this basin is proposed through integrated analysis, determining the ecological flow targets as 0.045 m³/s during the non-flood season (December to June) and 0.500 m³/s during the flood season (July to November). Except for exceptional years, the assurance rate of the daily average flow throughout the year should not be less than 90%. The research results can provide references for ecological flow assurance, optimal allocation, and regulation management of water resources in this basin.