As studies on ecosystem services progress from "static stock" to "dynamic flow", scientists gradually realize that ecosystem service flows (ESFs) constitute a key foundation for the scientific evaluation of ecological security at the regional scale. However, as modeling ESFs presents notable difficulties, how to consider ESFs in ecological security studies remains to be explored. Taking the Loess Plateau (LP) as the study area, this study incorporates water provision service flow into the ecological security assessment framework. The ecological security at multiple scales, combined with different climate and water provision service supply and demand scenarios, was assessed and compared for 2020 and 2030, respectively. The results show that: (1) Incorporating water provision service flow leads to an enhancement in ecological security in 2020 in LP, and this will be strengthened at the county scale. (2) The ecological security of the LP in 2030 is more sensitive to changes in water provision service supply scenarios, and this sensitivity increases progressively from the watershed to the county scale. (3) Ecological protection water supply scenarios can buffer the detrimental influence of climate change on ecological security in 2030, and conservation water demand scenarios effectively increase the ecological security level under the same water supply scenarios. The study emphasizes that in arid and semiarid areas, a dynamic assessment framework that integrates ESFs is a flexible way to identify regional ecological security, and also provides a more targeted decision-making basis for future ecosystem management and regional policymaking.