Soil-rock mixtures (SRMs) are identified as the main constituent material of landslides along the Duku High-way. Their shear mechanical behavior is highly sensitive to variations in moisture content. The K652 SRM landslide along the Duku Highway was selected as the research object. Direct shear tests on SRMs with dif-ferent moisture contents were conducted using a self-modified large-scale direct shear apparatus. The Particle Image Velocimetry (PIV) system was applied to measure the internal particle movement during the entire shear process. A three-dimensional Particle Flow Code (PFC3D) numerical model was constructed via exper-imental inversion. Meso-mechanism analysis was performed with the established model. The influence of moisture content on the shear mechanical properties of SRMs was revealed from both macroscopic and mesoscopic scales. The shear deformation and failure mechanism of SRM specimens are manifested as the dynamic evolution trend of contact force chains under external load. The essential effect of moisture content on SRM strength is the regulation of force chain strength and distribution by altering the interlocking effect between soil and rock particles. A shear influence zone is formed by block movement. Its range and duration are adjusted with the changes of force chain strength and density.When moisture content increases from 2% to the optimum moisture content (6.2%), the interlocking effect between soil and rock is gradually enhanced. The cohesion and internal friction angle of the specimens are improved. The peak shear strength is higher and more stable. The thickness of the shear influence zone is increased by approximately 31%. Particles are not prone to rotate. The contact force chain reaches the maximum density and is difficult to convert into a weak force chain. Therefore, the shear strength increases gradually with a slight variation trend.Under high mois-ture content conditions (8% and 10%), the shear strength of SRMs is significantly reduced. The peak shear strength at 10% moisture content is decreased by up to 42.9% compared with that at the optimum moisture content. The force chain network is softened rapidly after rapid strengthening. The thickness of the shear in-fluence zone is reduced by about 70%. Significant rotational displacement of particles is observed. The inter-locking effect is weak. Weak force chains dominate the whole shear process.The strength degradation mecha-nism of SRMs with different moisture contents in alpine regions is revealed by the test results. Technical guidance and theoretical support are provided for the disaster mechanism analysis and comprehensive preven-tion and control of snowmelt or rainfall-induced landslides along the Duku Highway and similar highways in alpine regions.