Abstract: The protection of river sources is of great significance to regional water security. How to extract key information from river sources and construct an assessment system is one of the key and difficult points in the research on the zoning control system for water ecological environment. The paper deeply analyzed the supply and demand relationship between river sources and human activities in water cycle and ecosystem service theory, integrated ecosystem service assessment methods into the zoning of water ecological environment, proposed a method for evaluating and delineating priority protection areas for river sources based on the relationship between water resource supply and demand, and applied it to the Moyang River Basin. The results showed that: (1) Based on research methods such as the supply and demand and circulation pattern of ecosystem services, the functional volume accounting of water resource supply services, and the importance indices calculating and grading, and using the spatial superposition operation function of ArcGIS software, indicators such as self-water sufficiency status (SWS) and water resource supply service path length (TL) were calculated by administrative village (community). Through SWS and TL, the water resource supply, demand and circulation pattern within the basin can be accurately depicted. The river source protection importance index, calculated based on weighted SWS and TL, can effectively represent regional differences within the basin. (2) According to the basin evaluation, Moyang River Basin was divided into five levels according to the importance index, that was extremely important areas, relatively important areas, general important areas, ecological development areas, and urban development areas, with area proportions of 17.8%, 36.9%, 36.6%, 7.2%, and 1.5%, respectively. The extremely important areas mainly included the catchment area from the source of the Moyang River to Dahe Reservoir and the high rainfall area in the west of Tianlu Mountain. The relatively important areas included the contiguous mountainous areas surrounding the extremely important areas and the upstream contiguous mountainous areas of the Tanshui River. The general important areas were mostly agricultural areas in plain regions. The ecological development areas were large towns in the upstream and midstream, as well as large towns around the main urban area of Yangjiang City, while the urban development areas were the main urban area of Yangjiang City downstream. The five-level zoning showed a good gradient distribution in statistical indicators related to water resource supply and development utilization, establishing a water ecological environmental zoning control pattern for the entire basin that connected upstream water resource supply with downstream water resource utilization. (3) It was recommended that the contiguous extremely important areas of the Moyang River Basin be designated as priority protection zones for river sources, with an emphasis on strengthening the construction of water-conserving forests. Additionally, key biodiversity areas such as the Baichong Nature Reserve should receive special protection. Efforts to protect and restore key protected plants, endemic species, and key protected animals, along with their habitats, should be intensified.