Abstract: The grassland ecosystems encompass ecological functions such as biodiversity and water retention, as well as forage production. It is of great significance to understand the trade-offs and synergies among these functions, so as to achieve win-win outcomes in ecological conservation and pastoral welfare. In this study, the monetary values of both productive and ecological functions from 1980 to 2020 in the Three-River Headwaters Region (including the National Park and surrounding zones) were quantitatively analyzed. According to the results, (1) During 1980—2020, the average annual multifunctional ecosystem value in this region reached 8.18×10¹⁰ Yuan and presented an increasing trend (annual increase of 1.278×10⁹ Yuan), which was primarily driven by changes in grassland provisioning service (7.14 Yuan hm^-2 a^-1). When cultural functions were included, the average total value reached 1.186×10¹¹ Yuan during 2018—2020, in which the ecological functions accounted for 77%. (2) Ecosystem service values exhibited significant spatial heterogeneity: The overall distribution pattern decreased from southeast to northwest, in which the southeastern region showed high values in water retention (48.17% of ecological functions) and soil retention, the western and northeastern regions displayed prominent wind-sand fixation values, and the eastern region demonstrated high grassland provisioning values due to favorable hydrothermal conditions. (3) The relationships among functions varied across temporal and spatial scales: Temporally, grassland provisioning services were synergistically related with overall ecological functions; spatially, western regions were characterized by synergistic relationships, while eastern and southern regions exhibited trade-offs, particularly in the agro-pastoral ecotone with significant trade-offs between wind-sand fixation and water retention and soil retention functions. This study provides a scientific foundation for developing regional development and ecological conservation management plans based on the grassland multifunctionality.