[Objective]Located in the transitional zone between the Qinghai-Tibet Plateau and the Loess Plateau, the Tao River Basin exhibits distinctive geomorphological features shaped by the combined effects of these two plateaus. As a critical ecological barrier, it plays a pivotal role in providing key ecosystem services such as water conservation, it is of great theoretical and practical significance to explore the spatial differentiation of ecosystem service value and driving factors of watershed topographic gradient to realize the sustainable development of watershed.[method]This study employed six phases of land-use remote sensing data (1993–2023) and integrated the ecosystem service value (ESV) assessment model, terrain distribution index, and geographical detector method to systematically explore the spatial and temporal evolution law, the topographic gradient characteristics and driving mechanism of ecosystem service value in recent 30 years. [Results]The results reveal that: (1) The basin displays a typical stepped topographic gradient distribution, with 84.99% of its area concentrated in gradients 2–7. Dominant land-use types across gradients 1–9 follow a sequential transition: construction land–water bodies–cropland–grassland–forestland–forestland–forestland–unused land–unused land. (2) The total ESV increased by 6.39×10?yuan (a 2.36% rise). Its spatial distribution shows a gradient differentiation characteristic of first increasing and then decreasing along the terrain gradient from low to high. High ESV values were predominantly distributed in gradients 5 and 7 (adjacent to the Qinghai-Tibet Plateau), while low values clustered in gradient 1 and gradient 9 regions within the southwestern Loess Plateau. (3) ESV gradient differentiation arises from the synergistic interaction of natural geographic and socioeconomic factors, with elevation (DEM) serving as the dominant explanatory factor (q = 0.491). Its interactions with slope and land-use intensity demonstrate two-factor enhancement effects. [Conclusion]This study clarifies the topographic gradient response characteristics of ecosystem service values in mountainous transitional zones, offering scientific insights for optimizing ecological spatial management and advancing regional sustainable development in river basins.