The formation mechanisms,movement processes,and dynamic characteristics of debris flow in the Western Sichuan Plateau,a high altitude and cold climate area,are unique because of the effects of landform,geological structure,ormation lithology and climate conditions.The areas of water convergence,provenance and accumulation of debris flows in the Sitongda Valley,Ganzi County,Sichuan Province are investigated by field investigation,mapping and sieving test to determine their formation mechanisms and dynamic characteristics.Results indicate that:(1) There are a big difference in elevation of basin terrain and a high ratio of channel slope,which provides terrain conditions for formatting debris flow.(2)Because drainage area of debris flows is wide,short-term rainstorm in plateau climate is able to provide adequate water supply.(3)Rivers develop in more than 3 000 maltitude areas, located in a climate change belt within cold temperate,subfrigid and frigid zones.Rock mass is fractured and soil structure is loose,caused by the climate condition of strong sunshine and large difference temperature that makes rock contrast weathering strong,as well as the influence of Xianshuihe fault zone.The fractured rock mass and loss soil structure provide rich source for the formation of debris flow.