Abstract: Tectonic mélange zones are extensively distributed along the eastern margin of the Tibetan Plateau in China, and often form soft-base slopes, which are highly prone to instability under both internal and external dynamic forces.Such instability poses significant constraints on the implementation of national strategic projects, including cascade hydropower development and transportation corridors.Investigating the formation mechanisms of soft-base landslides within tectonic mélange zones is therefore crucial for disaster prevention and mitigation, carrying important theoretical and practical significance.Focusing on the Baige landslide, we employ detailed field investigations, large-scale geotechnical centrifuge physical modeling, and numerical simulations to explore the failure mechanisms of soft-base landslides in tectonic mélange zones.The results indicate that the original slope of the Baige landslide is a typical soft-base slope.Its deformation and evolution process can be divided into four stages: creeping compression and downward dislocation, development and propagation of fractures and altered clay, dilatant uplift of the locked segment, and shearing-off of the locked segment and landslide initiation.The lithological combination of the slope is the fundamental factor controlling its failure mode.The serpentinite zone acts as a soft base, undergoing settlement creep under long-term gravitational stress, further leads to subsidence at the slope crest and continuous development and propagation of transverse cracks.Simultaneously, the upper rock mass persistently creeps and compresses the underlying locked segment that obstructs sliding, causing its shearing uplift.Over time, joints within the slope gradually connect, forming a slip surface.Eventually, the locked segment at the base shears off, triggering the Baige landslide along with the sliding of the rock and soil mass in the main slip zone.The findings of this study provide a scientific basis for disaster prevention and mitigation of soft-base landslides.