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At approximately 7:00 p.m. on January 3, 2022, a bedding landslide (referred to as the Jinhaihu landslide in this paper) occurred in the Jinhaihu District of Bijie city, Guizhou Province, China, resulting in the death of 14 laborers. The catastrophic landslides induced by the geological conditions in the study area are incomprehensible and deserve an in-depth study of their genetic mechanisms. In this paper, a detailed field investigation was conducted on the Jinhaihu landslide, and the geological background of the landslide area and the characteristics of the landslide were well revealed. The slide zone and rock samples of the landslide site were obtained for physical and mechanical tests to further establish a coupled PFC/FLAC2D model of the landslide area and analyze the genetic mechanism of the Jinhaihu landslide using numerical simulation. The results indicate that the landslide area has been disturbed by long-term engineering, and a large amount of excavation at the foot of the slope has reduced the resistance of the landslide to slide downward, increased the damage to the slope, and provided space for the landslide to move. However, the excavation did not immediately initiate the landslide at the toe, and the claystone containing a large number of illite clay minerals (56.5%) gradually weakened with the infiltration of rainfall before the slope finally failed. The numerical simulation indicated that the excavation at the toe of the slope caused cracks at the crown, the softening of the claystone caused the sliding mass to be divided into blocks by the cracks, and then the sliding mass slid downward along the weak interlayer. First, the sliding mass toppled down and disintegrated at the front edge, and the rear of the sliding mass was tensile-fractured and failed. The movement of the rock blocks on the slide bed has the character of translation with almost no rotation. The evolution process of landslides is divided into four stages: the initial stage, fracture generation stage, softening stage and overall failure stage. The research results of this paper provide a reference for the risk evaluation and disaster prevention of the same category of landslides.