The reactivated Lijie North Mountain landslide in Zhouqu County, Gansu Province, has triggered repeated debris flows with ongoing creep deformation, posing significant threats to adjacent villages, roads, and downstream areas. By integrating field investigations, satellite imagery analysis, global navigation satellite system, and micro-deformation radar monitoring, this study reveals the landslide’s developmental features, deformation process, evolutionary trend, and genetic mechanism. Results are as follows: (1) The Lijie North Mountain slope exhibits a polyline profile (steep upper/lower sections, gentle midsection, and flat base) with a maximum elevation difference of 1 450 m, forming a large high-position colluvial landslide under multifactor coupling. (2) Comprising 10 ancient/recent sliding zones with complex interactions and failure modes, the landslide exhibits a multistage retrogressive failure pattern characterized by sequential bottom-up progression where frontal sliding mechanically destabilizes rear blocks, leading to a headward erosion mechanism. (3) Influenced by tectonic structure, topography, and rainfall, the landslide exhibits an integral instability potential, forming a cascading hazard chain (landslide-debris flow-barrier lake). Multisource monitoring integrated with landslide characteristics enables an accurate interpretation of the deformation process and a mechanistic analysis, providing a scientific basis for the early warning and mitigation of analogous high-position accumulation landslides.