Abstract: A rainstorm triggered debris flow hazard occurred in Hongchun valley, Yingxiu town on August 14,2010. This event transported 805,000 m3 material sediment to the watercourse of the Minjiang River and produced a natural dam,resulting in a flash flood in the new Yingxiu town. It buried the national highway 213 out of the vallay for 400m and the roadbed and many piers of the Yingxiu-Wenchuan road that wad on building. 17 people were missing. The Hongchun vallay debris flow was one of the typical debris flow gullies occurred in the last years according to the survey after the hazard. The centralized provenance was particularly rich after the earthquake, the flow solid matter volume was huge once as the debris flows in progress and the character of multi-point dam-breaking and pull trough incised to start the provenance was very obvious, what was found in the survey. This paper is selective analysis. The three conditions for the formation of debris flow debris flow movement mechanism is analyzed and the motion characteristic parameters is inversed,forecasting the trend of its development.