Abstract: A study was conducted on the relationship between the formation and development of the "8·7" flash flood and debris flow disaster in Yuzhong County, Gansu Province in 2025 and extreme rainfall and water conditions, using methods such as unmanned aerial vehicles, on-site geological surveys, data collection, and hydrological survey calculations. The results show that the "8·7" flash flood in Yuzhong, Gansu Province occurred in the special landform area of "two mountains with one basin". The extreme rainstorm triggered flash flood, landslide and debris flow, which formed a huge flash flood and debris flow. The overall characteristics of the flash flood and debris flow are extreme, complex, difficult to predict, hidden and destructive. The rainfall duration in the upper and middle reaches of the Kangu River and Xinglong River basins is long, with a cumulative precipitation of 119.4～220.2 mm. The peak flow of the basin has exceeded the historical maximum peak flow of 161 m³/s at the Yuzhong County hydrological station. There are two peak values for precipitation and mountain flood, with the mountain flood peak lagging behind the maximum rainfall peak by about 2 hours. The flash flood triggered by the second precipitation triggered debris flow disasters. Flash floods and mudslides form in the middle and upper reaches of the watershed. The trees washed down by flash floods and mudslides form wooden and stone blockages, causing local canyon sections to rise in water levels. The living environment of some river channels in the middle and lower reaches amplifies the disaster effect.