Abstract: [Objective]At 8:40 am on July 17, 2024, the Wanshuitian landslide in Jiajiadian Village, Guizhou Town, Zigui County, became unstable and failed, with a total volume of approximately 800,000 m3, resulting in the destruction of 1,200 meters of village-level roads and 60 mu of agricultural and forestry citrus orchards. The landslide exhibited a high degree of concealment and a strong suddenness. [Methods]This paper, through detailed field geological surveys, drone aerial photography, and monitoring data analysis, and based on the analysis of the movement characteristics of the Wanshuitian landslide, combines the Geo-Studio finite element simulation software to calculate the internal seepage characteristics and slope stability evolution process of the landslide under heavy rainfall conditions, thereby revealing its genetic mechanism and failure mode. [Results]The results indicate that the Wanshuitian landslide is a high-speed rock landslide, which can be divided into five subzones based on its movement characteristics: the initiation zone, the secondary disintegration zone, the main accumulation zone, the right scattering zone, and the left scattering zone. The intrinsic factors contributing to the occurrence of the Wanshuitian landslide include the lithology of interbedded sandstone and mudstone, the microtopography of alternating ridges and troughs, and the jointed rock mass structure. The primary external factor was the two rounds of continuous heavy rainfall, with a cumulative rainfall of 253.8 mm over 17 days prior to the landslide. The continuous heavy rainfall led to a sustained increase in pore water pressure within the slope, significantly reducing its stability. After two rounds of heavy rainfall, the pore water pressure in the sliding body and the sliding zone rock and soil mass increased substantially, with the maximum pore pressure reaching 75.4 kPa and the maximum pore pressure increment reaching 303.9 kPa. The sudden increase in pore water pressure ultimately triggered the landslide instability and failure. In the case of the Wanshuitian landslide, due to the obstruction of sliding in the direction of the rock layer dip, the slope body slid along the free surface. The main sliding direction of 10° formed an 88° angle with the rock layer dip direction of 282°, resulting in a unique failure mode of nearly sliding along the rock layer strike. This mechanism significantly differs from the instability mechanism of bedding landslides, characterized by high concealment and strong suddenness. [Conclusion]The research findings are of great significance for disaster prevention and mitigation efforts at potential hazard sites with similar conditions in mountainous areas of China.