<p>Discontinuities at different scales present considerable obstacles in achieving precise and efficient slope stability analysis. This study aims to address this critical challenge by incorporating multi-scale discontinuity effects in the slope structural geological model and conducting 3D fracture connectivity evaluation. Through the high-resolution 3D digital outcrop model of a high-steep slope in Lhorong County, acquired by unmanned aerial vehicle (UAV) photogrammetry, the orientations, sizes, and locations of exposed multi-scale discontinuities were analysed. A novel processing scheme that explicitly represents large- and medium-scale discontinuities via discrete fracture networks while homogenizing small-scale discontinuities into equivalent rock mass parameters was proposed to reflect their influence on slope stability. Subsequently, the slope multi-scale structural geological model was established and 3D fracture connectivity analysis was utilized to explore the potential critical slip surface (CSS). When the entry points of the CSS are situated in the mid-upper section of the slope, the factor of safety (FOS) exhibits slow fluctuation (1.92 ~ 2.00), revealing a geomechanically sensitive zone where the CSS preferentially occurs. The location and shape of the CSS are considerably controlled by the large-scale discontinuities, and the real failure boundary may lie beneath the CSS acquired by the proposed method. Nevertheless, the method advances preliminary slope stability assessment by resolving multi-scale discontinuity interactions while maintaining computational efficiency and accuracy, providing a paradigm for high-steep rock slopes.</p>