<p>Ecosystem services (ESs) strongly impact ecosystem functions and show relationships with human well-being and land use/cover change (LUCC). However, studies on ecosystem evolution and the driving factors in reservoir basins remain relatively limited. By adopting the Miyun Reservoir Basin (MRB), Beijing, as a case study, this study examined LUCC from a past and future perspective — analyzing historical changes between 1980 and 2020, and applying the Patch-generated Land Use Simulation (PLUS) model to investigate three scenarios for 2050. The geographically weighted regression (GWR) and Integrated Valuation of Ecosystem Services and Trade-offs (InVEST) models were applied to examine spatiotemporal variations in ESs and to quantify the impacts of trade-offs and synergies between pairs of ESs. Finally, a GeoDetector was applied to identify the mechanisms under which relationships between pairs of ESs change. There were significant alterations in MRB land use between 1980 and 2020, with the highest alterations in forest and construction land; the ecological protection (EP) and natural development (ND) scenarios were associated with the least and greatest land expansion, respectively. There was spatial heterogeneity in ESs, mostly in water yield and habitat quality, showing peaks in the west and northeast; the cultivated land protection (CP) and EP scenarios were associated with the greatest declines in water yield; habitat quality increased under the EP scenario. There were significant differences in synergistic and trade-off relationships between pairs of ESs in the MRB. These differences could be mainly attributed to natural factors, including elevation, evapotranspiration, and temperature. The results of this study provide a scientific foundation for ecosystem service regulation in water source areas and ecological management in river basins.</p>