Abstract: Ancient fording landslide is a common disaster for hydropower projects in Southwest China. Revealing the disaster mechanism of such landslides is helpful for reduction of the risk probabi-lity of chained disaster. Taking the Lajinshengu landslide in Deqin County of Yunan Province as an example and based on the field geological survey, Synthetic Aperture Radar Interferometry (InSAR) and numerical modeling, the authors in this paper analysed the formation characteristics and the failure progress of the landslide, combining with the engineering geological elements of the landslide area. The result show that: ① The disaster processes of Lajinshengu landslide are the local deformation stage of the front, tension stage of trailing edge, sliding--barrier lake stage and collapse stage of the barrier lake. ② The direct reasons for the landslide deformation are synergy of rising water level and rainfall. ③ The possibility of a landslide blocking chain disaster is very high, if the geological environment of the landslide continues to deteriorate. The InSAR and other monitoring techniques are suggested to carry out the early identification of similar wading ancient landslides in this paper through the study of the disaster mechanism of the ancient landslide in the Lajinshengu landslide, which are of great significance to reduce the risk caused by chain disasters.