Abstract: The Yellow River water supply area in Gannan functions as a critical ecological barrier in the upper reaches of the river, playing an irreplaceable role in water conservation and soil retention within highland wetlands, and playing an indispensable role in maintaining the stability and balance of the upper Yellow River ecosystem. Clarifying the supply-demand relationships of ecosystem services (ESs) in this region is essential for achieving the national strategy of "Ecological Protection and High-quality Development of the Yellow River Basin". This study employs the InVEST model and ArcGIS to systematically examine the spatiotemporal dynamics of ecosystem service supply, demand, and their matching patterns in the Gannan water supply area from the year 2000 to 2020, with a focus on water conservation, soil retention, food provision, and carbon sequestration. The results show that: (1) In the temporal dimension, both supply and demand of all ESs increased, with supply consistently exceeding demand. In the spatial dimension, clear heterogeneity was observed. Water conservation and soil retention services exhibited a "southwest high-northeast low" distribution, whereas food provision and carbon sequestration showed a "north high-south low" pattern. Except for soil retention, the demand for ESs followed a "northeast high-southwest low" distribution. (2) The supply-demand ratio of water conservation and food provision increased over time, while that of soil retention and carbon sequestration declined. Water conservation, food provision, and carbon sequestration remained in a surplus state, with expanding of areas of supply exceeding demand; by contrast, soil retention persistently exhibited a deficit, and the areas where demand outpaced supply continued to expand. (3) Spatial matching analysis indicate that soil retention was dominated by low-supply-high-demand mismatch areas, water conservation and food provision by high-supply-low-demand mismatch areas, and carbon sequestration by low-supply-low-demand matching areas. Targeted management strategies are proposed for different matching types: in high-high areas, the focus should be on optimizing land-use structure, enhancing ecological and economic benefits, and safeguarding existing resources; high-low mismatch areas should prioritize degraded grassland restoration, promote ecological animal husbandry and tourism, and foster eco-economic coordination; low-high mismatch areas should strengthen intensive land use, develop modern agriculture, and improve land-use efficiency; and low-low matching areas should prioritize natural ecosystem restoration, strengthen protection, and regulate human activities to enhance sustainable development potential.