Based on the survey results of flash flood impact, this paper evaluated the flood influence in the Luxi reach of the Chang River and established the water level warning index system and a hydrologic forecasting model. The main conclusions in - clude: (1), the risk of flood is less than once in every five years in the Luxi reach of the Chang River, which belongs to the typical area affected by the threat of flash flood; (2) the warning water level of flash flood in the Luxi reach is 75.5m; and (3) the re - al-time and forecasting results of the Luxi station can be used as the guidance of flood warning for the adjacent reaches. The method of evaluation and framework of warning system can be used as a reference for improving the non-engineering measures a - gainst flash flood disasters and operational application of hydrology monitoring system in small and medium-sized rivers.