On August 11,2005,an extremely wide debris flow disaster with return period of more than 100 years took place in the Hailuo Valley,Luding County,the east of the Gongga Mountain.After investigation of the disaster, the causes of the disaster occurrence,including geology,relief,climate and human activities,were analyzed.The main cause to the occurrence was the heavy rainstorm.The amount of daily rainfall was over 88 mm on August 12.The trend of debris flow activities was analyzed by referring to historical debris flow.Controlling countermeasures such as emergency measures and upper mitigation measures are presented through comparing the 050811 hazard with other hazards like the debris flow in Xinping County.