Abstract: Typhoon rainstorm-triggered debris flows exhibit high suddenness, mass occurrence, and destructiveness.Therefore, researching the initiation mechanisms of this specific type of debris flow is particularly crucial.Taking the debris flow disaster in the reservoir area of Anhui Ningguo Pumped Storage Power Station triggered by Typhoon “Lekima” as a typical case, the characteristics, formation conditions, and sediment distribution of debris flow gullies were identified based on field explorations, investigations, and tests.Utilizing the physical model test of artificial rainfall, the changes in indicators such as pore water pressure, volumetric water content, soil pressure, and erosion characteristics were monitored during the rainfall, thus the initiation mechanism of typhoon rainstorm-triggered debris flow was studied.The results showed that:(1) The outbreak of the typhoon rainstorm-triggered debris flow can be divided into four stages, namely rainfall infiltration, super-saturation runoff, erosion and accumulation of sediment sources, and initiation under short-duration intense rainfall.(2) The typhoon rainstorm-triggered debris flow occurs after shallow soil reaches high water content and high pore water pressure, which requires a certain amount of accumulated rainfall beforehand.(3) Under conditions of lower rainfall intensity, watery debris flows may occur in the gully; however, a sudden increase in rainfall intensity intensifies runoff and erosion significantly, initiating a large amount of solid material.The debris flow transits from watery to viscous, with visible large-scale accumulation fans accumulating at the gully mouth.(4) Penetration of varying degrees among eroded channels was observed throughout the gully, and the erosion depths increased with the decreasing elevation.These findings can provide insights into the prevention and control of typhoon rainstorm-triggered debris flow disasters.