Abstract: Through the field investigation and analysis on the Sanyanyu and Luojiayu valley debris flow happened in Zhouqu county,Gansu province on August 8,2010,the paper thought that the sudden strong rainfall,the alpine gorge landform and the rich loose deposits are the three basic conditions which caused the debris flow disaster.The disaster characteristics included three aspects.Firstly,the drainage channel was occupied excessively by the building in stack area,so the flood discharge capacity is insufficient.Secondly,the step by step failure of the natural rock fill dam and artificial blocking dam in transportation zone caused a "domino effect" type of damage.Thirdly,the debris flow blocked Bailong river and formed barrier lake.It submerged county and aggravated the debris flow disaster.Zhouqu debris flow disaster is very typical and rare,hence,it is meaningful to reveal its disaster characteristics for the post-disaster treatment.