Seven landslides among the 110 landslides on the northeastern margin of the Tibetan Plateau in China were selected to analyze the structural development processes within the shear zones. In addition, the platy clay mineral content and mineralogical composition of the shear zone were also investigated. The samples obtained from the vertical profiles were quantitatively studied from top to bottom with respect to their material composition, pore structure, and water properties to understand the changes in the cementation and frictional properties of the shear zone. The results indicate that the structure is progressively modified by fractures, cleavage, and plasticization. Even though there is no sliding surface liquefaction, clayey particles are observed to exhibit slipping and rearrangement. The illite–montmorillonite mixed-mineral layer accumulates near sliding surface in the core zone, and the platy clay minerals are arranged along shearing direction for long shear displacement.