Abstract: A valley-typed debris flow ditch occurs in the downstream Yalongjiang River.Its frequency of outbreaks is generally 7 to 10 years.On the morning of July 1,2008,a concentrated rainfall less than the biggest daily rainfall in the valley within a few years ago has caused a debris flow hazards.Through the analysis of the survey,the main reason for this is that the valley has broad drainage area and a steeper longitudinal drop,plus a large number of excavation wastes that heaped directly in the trench caused by plugging since 2007.Under a heavy rainfall caused flooding,the rockfill dam was destroyed,the secondary-induced outburst floods that achieved a peak flow of the 10-year storm level stimulated the lower narrow channel deposits being a debris flow.Due to the confined channel in the plant,the debris flow that overstepped in the curve way burst into the workshop and caused a significant property damage.