Tectonic suture zones on the Tibetan Plateau, as structurally weak belts, commonly host numerous large to very large rockslides. However, how the material composition and structural architecture of suture zones govern the initiation and evolution of landslides remains poorly understood. This study focuses on the Jinsha River suture zone (JSSZ). Through systematic field geological investigations, laboratory microstructural analyses, and landslide inventory statistics, we elucidate the control of tectonic mélange belt lithology and structure on landslide development, and construct a four-stage dynamic conceptual model from initiation to triggering. The results indicate that the heterogeneous, weak lithologies and complex structures of the suture zone provide the fundamental material and structural basis for landslide initiation. Sliding surfaces are not randomly distributed but predominantly localized along sub-horizontal foliation planes or lithological interfaces. These pre-existing discontinuities, under tectonic uplift and river incision, become preferential pathways for stress release and progressive weakening, resulting in clustered landslide distribution along the suture zone. Accordingly, a four-stage initiation and evolution model is proposed, systematically explaining the complete dynamic process from suture zone formation establishing the material-structural framework, through tectonic uplift and river incision driving rock mass fracturing, freeze–thaw cycles and chemical weathering causing progressive coalescence of the sliding surface, to final triggering of catastrophic failure. This study reveals the fundamental control of suture zone lithology and structure on landslide initiation, shifting the analytical perspective from short-term triggers to long-term dynamic coupling, and from external driving conditions to intrinsic lithological-structural constraints. The findings provide a new theoretical framework for understanding clustered rockslide development on the Tibetan Plateau and similar active orogenic belts, and offer a material-structure-based assessment basis for major engineering site selection and early risk identification.