Abstract: The Wudongde Reservoir area has the characteristics of intensive development of landslides in the red bed reservoir section.Taking the Xiaochatou landslide in the Wudongde Reservoir area as an example, the influence of the formation of the ancient barrier lake on the development of the red bed landslides in the reservoir area was explored.The red bed rock samples were taken for mineral analysis and mineral identification.The sandstone and conglomerate were soaked in deionized water to analyze the microstructure and dissolved ion concentration of the rock mass in different soaking stages, and the wave velocity changes of mudstone under wet and dry cycles were measured.On this basis, the GeoStudio numerical simulation software was used to calculate the failure process of the slope under the action of fluid-structure interaction.Studies showed that gypsum in sandstone and conglomerate was easily to dissolve in water to form dissolution holes and thus enhanced permeability; the concentration of SO42- ions in the soaking solution was the largest, followed by Ca2+,Na+,so gypsum was the main dissolved mineral; after four wet and dry cycles, part of the thin layer on the mudstone surface fell off, micro-cracks were formed, and the wave speed was significantly reduced; the deformation mode of the landslide was sliding-pressing and pulling, and the rupture surface of the landslide was stepped-like.In this mode, the mudstone acted as a control slip layer, generating cracks of narrow upper end and wide lower end in the sandstone and making them expand and extend upwards until the slope rock mass was unstable and damaged.