Abstract: Watershed ecosystems, as complex ecosystems where human and natural systems are highly intertwined, play a critical role in agricultural water security through their multi-hydrological functionalities. This paper first dissected the concepts of multi-hydrological functions within watershed ecosystems and agricultural water security. The multi-hydrological functions encompass water source conservation, freshwater supply, runoff regulation, and water quality purification, while agricultural water security refers to the controllability of water quantity, quality, supply reliability, and water-related disaster losses in agricultural production. Subsequently, we explored the impact of each hydrological function on agricultural water supply safety, water quality safety, and water disaster prevention. Ecosystems such as forests, grasslands, and wetlands perform significant roles in water source conservation, freshwater supply, runoff regulation, and water quality purification, which can increase the amount of water available for agriculture, reduce the risks of floods and droughts, as well as soil erosion, and mitigate agricultural pollution, thereby enhancing the level of water security for agriculture within the watershed. There is a trade-off and synergy between the multi-hydrological functions of watershed ecosystems and the safeguarding of agricultural water security. Engaging in ecosystem protection, restoration, and enhancement of multi-hydrological functions is crucial for ensuring the safety of agricultural water use. Considering the existing research gaps, further research is proposed in the areas of mechanism studies, model development, and practical applications. This includes exploring the interrelationship and coupling mechanisms between hydrological multifunctionality and agricultural water security, developing coupled hydrological models, and conducting ecosystem protection, restoration practices and landscape optimization for improving ecosystem hydrological multifunctionality. The aim is to provide scientific support for the safeguarding of agricultural water security and sustainable development from the perspective of ecological barrier functions.