The Bailongjiang watershed (BLJW) is an important water conservation area and ecological barrier of the upper Yangtze River. It also has a concentrated area of national-level poverty-stricken counties. To explore the spatial characteristics of ecosystem services in a catchment scale, we analyzed the distribution characteristics of typical ecosystem services in a terrain gradient using the ArcGIS software and InVEST model, from the perspective of elevation, slope, landform relief and terrain niche. The results indicated that there were apparent differences in the spatial distribution patterns of carbon storage, water conservation, habitat quality, and soil conservation services of the BLJW in Gansu, where the areas with a high ecosystem service value were mainly distributed in the nature reserves and forest areas, while the areas with a low service value were mainly distributed in the river valleys, towns, and farmland areas. Further, it was observed that the carbon storage, water conservation, and habitat quality increased with an increase in the slope and topographic fluctuation, while the soil conservation service increased at first and later decreased with an increase in the topographic position index. The important areas of the integrated ecosystem service gradually polarized in the BLJW, and the important areas of the multiple ecosystem service supply were located in the areas having a middle and high topographic position. The topographic features are an important factor affecting the gradient distribution of the ecosystem services. The spatial distribution characteristics and relationships of four typical services were analyzed under different topographic factors in the BLJW. This can be used to provide a scientific base for an optimal ecosystem pattern and the construction of ecological civilization for the mountainous areas in western China.