Abstract: Determining the spatial and temporal relationship between ecosystem service supply and demand, and clarifying the dynamic mechanisms of service flows, plays an important role in promoting harmonious coexistence between humans and nature and achieving sustainable development. This study focused on the transitional zone between the Loess Plateau and the Qinghai-Tibet Plateau. Based on the InVEST model and relevant socio-economic multi-source data such as land use, soil, terrain, climate, etc., we assessed the supply and demand of carbon sequestration, food provision, water yield, and soil retention services. Ecosystem service flows were traced along wind directions, rivers, and road corridors to connect supply and demand areas. Consequently, we quantified the changes in flow volumes and classified the flow levels for carbon sequestration, food production, water yield, and soil retention services. The results showed that the supply of food production, water yield, and carbon sequestration services showed an increasing trend, with growth rates of 22%, 12%, and 2%, respectively, while soil retention service supply decreased by 27%. The demand for food production, water yield, carbon sequestration, and soil retention services increased, with growth rates of 152%, 16%, 225%, and 22%, respectively. The supply-demand index for food provision and water yield services rose by 51% and 19%, respectively, whereas carbon sequestration and soil retention services showed a decline of 71% and 46%, respectively. High soil retention and water yield flows were mainly distributed in the western regions, such as the Heihe River, Qinghai Lake, and Shiyang River basins. High carbon sequestration flows were concentrated in the eastern part of the study area. High food production flows were primarily located in the hilly areas of the eastern Loess Plateau, while the low service flows were distributed in Qingshui River and Kushui River basins. In the future development of the transition zone, the protection of carbon sequestration service supply areas and the restoration of demand areas can be strengthened, optimizing the regional supply-demand balance to achieve sustainable ecosystem development.