In the arid regions of Northwest China, vegetation cover plays a crucial role in maintaining unique terrestrial ecosystems. Vegetation growth is highly sensitive to variations in topographical factors, and the influence of topography on vegetation cover has attracted increasing attention. This study analyzed vegetation dynamics and their relationship with topography in the Tianshan Mountains of China using Landsat Normalized Difference Vegetation Index (NDVI) data during 2000-2022 and Shuttle Radar Topography Mission (SRTM)-derived topographical factors (elevation, slope, and aspect). Theil-Sen slope estimation and Mann-Kendall trend tests were applied to quantify temporal changes in vegetation, while a terrain area correction coefficient (K) was used to assess spatial associations of vegetation with topography. Random Forest (RF) regression and SHapley Additive exPlanations (SHAP) analysis evaluated the relative importance of topographical factors in shaping vegetation cover (multi-year mean NDVI) distribution. Key findings included that over the 23-a period, 59.46% of the vegetated area exhibited significant improvement (P<0.05), with the southern Tianshan Mountains showing the most pronounced increase (70.59%), whereas vegetation degradation (3.10%) was primarily concentrated in river valleys with intensive human activities. RF-SHAP analysis revealed that elevation is the primary driver of vegetation cover patterns, explaining 52.00% of the NDVI variation. The peak NDVI (0.42) occurred at elevations between 2800 and 3200 m. Slope and aspect also significantly influenced vegetation distribution, and higher NDVI values and greater improvement trends were observed on shady (north-facing) slopes compared to sunny (south-facing) slopes. K-index analysis indicated pronounced vegetation change-both degradation and improvement-in areas with elevations between 1100 and 2800 m and slopes exceeding 5 degrees, particularly on sunny slopes. Low-elevation desert areas in the southern Tianshan Mountains were highly susceptible to degradation. This study underscores the critical role of topography in regulating vegetation cover and its spatiotemporal dynamics, providing a scientific basis for sustainable management of arid mountain ecosystems.