Abstract:[Objective] The formation mechanism of rainstorm-induced debris flow in Yushu Plateau of Qinghai Province is researched. Which was expected to provide a basis for the prevention and control of debris flow disaster and reduction of the risk mitigation. [Methods] Through field survey, Lalong debris flow of Chengduo County in Yushu state was selected as an example, and the stimulus factors and mechanism were analyzed. [Results] The main channel length of the debris flow is about 3 km, the catchment area is 5.25 km2, the longitudinal gradient is 212‰, and the height difference is about 600 m. The volume of the landslide of the source area is about 6.50×104 m3, the volume of the debris flow is about 8.5×104 m3; and the volume of the material in the channel is 2.0×104 m3. [Conclusion] The process of rainstorm-induced debris flow in the study area can be divided into 4 stages: landslide-source formation, particle material starting up, gully erosion and debris flow initiation.