<p>In this study, the deadly August 12, 2015, Shanyang landslide is selected as a case study to explore the mechanical model and failure mechanism of the “apparent dip sliding” instability mode in this slope. Field engineering geological survey analysis revealed that the Shanyang landslide body comprises a driving block and a blocking block. The concepts of apparent dip sliding force and retaining-wall-like locking segments are introduced to establish a three-dimensional limit equilibrium analysis model of apparent dip sliding in the Shanyang landslide. The stability is then analyzed under conditions of long-term creep, argillization of the weak interlayer, and locking segment long-term damage. Using FLAC3D software, further analysis was conducted to determine the deformation characteristics and instability mechanisms of the apparent dip sliding in the Shanyang landslide. The results show the following: (1) During the apparent dip sliding process of the landslide, in addition to the argillization of the slip surface, the anti-sliding force of the true dip sidewall and the shear strength of the frontal locking segment are the key factors controlling the landslide. (2) The driving block first undergoes creep deformation towards the true dip direction, but the creep direction is deflected by a small angle in the NE direction affected by resistance from the frontal blocking block. (3) The cumulative damage to the locking segment of the Shanyang landslide leads to overall instability, forming a typical instability pattern of apparent dip sliding‒locking segment shear failure.</p>