Abstract: Slope monitoring in high-altitude cold-region mines is hindered by strongly dissected terrain, difficult deployment of ground instruments, and the line-of-sight (LOS) limitation of single-track InSAR. A steep mine slope near Lhasa, Tibet, was therefore investigated using 29 ascending Fucheng-1 images and 35 descending Sentinel-1 images acquired from August 2024 to October 2025. Separate SBAS-InSAR time-series analyses were first performed to compare the spatial resolution and temporal monitoring capability of the two datasets. A downslope-motion prior derived from DEM-based slope and aspect was then introduced. Weighted regularization was used to balance LOS-data fitting against the prior directional constraint, allowing east, north, and vertical displacement components to be estimated. Both datasets detected persistent deformation along valley flanks, in the middle and lower parts of the slope, near the slope toe, and within engineering-disturbed areas. Fucheng-1 delineated localized patch-like anomalies and their boundaries more clearly, whereas Sentinel-1 provided a stable representation of the regional deformation background. At representative point P3, the cumulative LOS displacement measured from ascending Fucheng-1 data exceeded 20 mm; P3 and P4 exhibited persistent or episodically accelerating deformation. Differences between ascending and descending LOS time series primarily reflect their distinct viewing geometries rather than inconsistency between the measurements. The three-dimensional solution indicates that the P3 landslide was dominated by horizontal movement, with comparatively weak vertical subsidence; the principal anomalies occurred in the central part, along the western boundary, and near the toe. These results demonstrate the complementarity of high-resolution domestic SAR and openly available Sentinel-1 observations. Integrating multi-source InSAR measurements with a weighted downslope prior improves the stability of three-dimensional deformation estimation under limited viewing geometry and supports hazard identification, priority-area screening, and dynamic monitoring of mine slopes in high-altitude cold regions of Tibet.