The Sela ancient landslide, located in the Jinshajiang suture belt, exhibits obvious signs of reactivation deformation, posing a significant risk of large- scale instability, potentially leading to a landslide, river blockage, and subsequent flood disaster chain. This study uses optical remote sensing dynamic monitoring, engineering geological surveys, and numerical simulation to analyze the reactivation deformation characteristics, simulate the stability, and predict the potential river- blocking outburst of the Sela ancient landslide. The results indicate that the Sela ancient landslide is a huge landslide with an estimated volume of 6300×104 to 9500×104 m3. The sliding mass comprises broken stone and soil, while the sliding bed consists of mica quartz schist belonging to the Permian to Lower Triassic Gangtuo Rock Group. The landslide displays obvious signs of reactivation deformation, currently in a stage of creep deformation. Continuous deformation has been observed from 2018 to 2023, mainly concentrated at the front edge of the slope. The Sela ancient landslide reactivates and slides along the pre- existing sliding surface, exhibiting traction- type progressive failure mechanisms. The stability analysis identified four potential instability modes. Under natural conditions, zone Ⅲ- 2 is unstable, with a landslide duration of about 35 seconds. The maximum landslide speed reaches 30 m/s. The resulting barrier dam would be approximately 97 m high, creating a barrier lake with a capacity of about 1.56×108 m3. The failure of this dam would generate a maximum flood flow of approximately 3650 m3/s and a maximum flood peak height of approximately 14 m at the Lava Power Station dam site. Similarly, under natural conditions, if zones Ⅲ- 3 zone or Ⅲ- 4 become unstable, the barrier dam height would be around 88 to 90 m, with a barrier lake capacity of approximately 1.22×108 m3. The dam failure would result in a maximum flood flow of approximately 2900 m3/s and a maximum flood peak height of approximately 12 m at the Lava Power Station dam site. Under earthquake conditions, simultaneous instability of zones Ⅱ and Ⅲ is predicted. This scenario would result in a barrier dam approximately 152 m high, creating a barrier lake with a capacity of about 5.88×108 m3. Dam failure would generate a maximum flood flow of approximately 19270 m3/s and a maximum flood peak height of approximately 44 m at the Lava Power Station dam site. To mitigate the potential casualties and property losses associated with this chain disaster, continuous monitoring of the Sela landslide using an integrated space- air- ground approach is strongly recommended.