<p>The mechanical response of the pile-soil interface in the Qinghai-Tibet Plateau permafrost under unidirectional freezing and freeze–thaw cycles is critical to ensuring engineering safety in cold regions. This study establishes a coupled water-thermal-force model to numerically simulate the evolution of temperature and displacement fields under these conditions. During unidirectional freezing, the temperature field propagates outward from the pile in a convex, arc-shaped profile. Both the freezing depth and thermal influence depth increase over time, with the latter being approximately three times the former near the pile. The pile head initially settles under load but subsequently experiences uplift, a phenomenon referred to as pile pull-out, due to frost heave. The final displacement is governed by the applied load. Under freeze–thaw cycles, significant thermal stratification develops near the interface, with isotherm spacing transitioning from dense to sparse as depth increases. Temperature fluctuations and their penetration depth are markedly greater near the pile than in the far field. The pile head displacement exhibits a cyclic pattern of rising then falling, superimposed on a gradual cumulative settlement, following a piecewise function with the number of cycles. These findings provide a theoretical basis for optimizing the design and ensuring the long-term safety of pile foundations in plateau permafrost regions.</p>