Abstract: In the early morning of August 21, 2023, flash floods broke out in the Lugaolin River Basin of Jinyang County of Sichuan Province, affected by short-term heavy rainfall, and the steel bar processing plant and the prefabricated houses of workers in the project encampment of the JN1（Jinning No. 1） bid section of the Yangtze River Expressway were washed away,resulting in 4 people killed and 48 people missing. After the disaster, the Sichuan Provincial Governments attached great importance to it and sent experts to investigate and evaluate the disaster process. Combined with the on-site investigation, the formation process and causes of the disaster were analyzed through hydrological and meteorological analysis and calculation,riverine flood discharge capacity calculation, etc., which can be used as a reference for the flash flood disaster prevention of similar projects.