Abstract: A large-scale,high-elevation landslide-debris flow struck Jinping Village,Mu'ai Town,Junlian County,Yibin City,Sichuan Province,on February 8,2025,causing severe casualties and property damage. By synthesizing on-site investigations,remote sensing interpretation,and monitoring data,this study reveals the formation mechanism of the disaster chain. The event occurred in a tectonic-erosional,medium-altitude mountain landscape at the transition from the Sichuan Basin to the Yunnan-Guizhou Plateau,featuring characteristic "L-shaped" high,steep topography with a 283-meter vertical drop from the headscarp to the shear outlet and an average slope of 42.7°. The complex regional geology of the area, located on the eastern margin of the Sichuan-Yunnan rhombic block near the Huaying Mountain fault zone,featured fractured rock mass and interbedded soft and hard strata, which provided potential sliding surfaces for landslide. Progressive deterioration of the rock mass was driven by winter freeze-thaw cycles under the influence of the"Kunming quasi-stationary front."The immediate trigger was exceptional persistent rainfall of over 300 mm since January 2025,which saturated the geomaterials,generated a surge in pore water pressure,and ultimately led to a sharp decrease in shear strength. The failure evolved through a chain process: fissure development-freeze-thaw degradation-rainfall infiltration-coalescent rupture-high-velocity movement-debris flow transformation,reaching a peak velocity of 56.29 m·s^-1. An emergency monitoring system combining slope radars and rockfall radars successfully predicted the secondary collapse on February 12,ensuring the safe evacuation of rescue teams. This research identifies a compound disaster-triggering pattern of"freeze-thaw degradation plus abnormal rainfall" in the Wumeng Mountains area,providing a scientific foundation for prevention and control of geological disasters in analogous regions.