On August 3, 2017, an outbreak of debris flow occurred in Dundo Town, Bomi County, Tibet. No debris flow occurred in the past 70 years. As a typical low-frequency debris flow in the Palongzangbo Basin, the causes of the outbreak were analyzed through on-site investigation. A large number of glacial melting water saturated the ice-water accumulation at the source of the gully. The internal friction coefficient and cohesion of the soil are greatly reduced, and the sudden collapse and large-scale landslides occur beyond the critical point of soil stability, resulting in a large number of ice-water deposits accumulated in the ditch entering the ditch to form debris flow. The flow rate, velocity and gravity are calculated by the method of morphological measurement and weighing method. Based on the analysis of the causes of the debris flow in Copenburmba, the causes of the low-frequency debris flow in Palongzangbu basin are discussed. It is concluded that most of the low-frequency debris flows in Palongzangbu basin are glacial debris flows, and that the debris flow gullies in the region will enter a new active period with multiple frequencies, multiple causes and different scale storms. Trend.