以北京市为例，对南水北调中线一期工程产生的实际生态效益进行定量评估。确立南水北调已建工程生态 效益评估方法，分析北京市南水北调供水对生态效益的贡献比例，围绕林地、城市绿地、湿地、压采地下水和水域 生态效益 5 个方面，计算南水北调中线一期工程为北京市带来的生态效益价值。结果表明：中线一期工程通水后 的 4 年间（2015—2018 年），北京市新增的林地、绿地、湿地、水域生态效益和补充地下水生态效益累计为 181.88 亿元，其中由中线一期工程供水累计新增的生态效益价值达到 67.31 亿元。进一步分析可知，在中线一期工程供 水产生的生态效益中：新增水域的生态效益最大，占比为 55.00%；压采地下水生态效益次之，占比为 34.85%；新增 林地和绿地生态效益占比分别为 6.91% 和 3.24%。研究结果可为北京市及其他南水北调受水区的生态用水、生态 环境修复与保护和资源高效利用等方面政策及措施的制定提供支撑。

As the most important basic strategic water resources allocation project in China, the South-to-North Water Transfer Project has completed the construction of the first phase of the east and middle route, and started supplying water from 2013 to 2014. Up to 14/05/2022, the cumulative water transfer of the first phase of the east and middle route has exceeded 53 billion m3.The South-to-North Water Transfer Project is playing an increasingly important supporting role for China's economic and social development and ecological and environmental protection. With the improvement of the strategic position of ecological civilization construction and the significant improvement of the requirements of ecological and environmental protection awareness, it is necessary to study, analyze and reasonably quantify the ecological benefits of the South-to-North Water Transfer Project, so as to provide a reference basis for the planning, construction, operation and management of the South-to-North Water Transfer Project and other inter-basin water transfer projects. Therefore, based on the principle of ecological economics, the ecological benefit evaluation indicators of the built projects of the South-to-North Water Transfer Project were defined, the basic data acquisition and processing methods of the ecological benefit evaluation methods of the built projects of the South-to-North Water Transfer Project were anailzed, Beijing was taken as a typical water receiving area, and the ecological benefits of the phase I project of the middle route of the South-to-North Water Transfer Project to Beijing were discussed, so as to provide technical reference for the ecological benefit evaluation of the built projects of the South-to-North Water Transfer Project. It is assumed that the ecological benefit of the South-to-North Water Transfer Project refers to the full utility of the beneficial effect caused by the change of ecosystem state due to the water supply from the project in the ecosystem and its influence range of the project area after water supply, which can be measured by the change of ecosystem service value. Therefore, the value of ecological services of the first phase of middle route of the South-to-North Water Transfer Project for Beijing City were evaluated by determining the evaluation method in 5 aspects including woodland, city green-land, wetland, groundwater and open water. Based on the statistical data of the capital landscaping government network of Beijing Landscaping Bureau, the basic situation of forest resources and urban green space in Beijing was obtained. The Landsat 8 remote sensing image data and its relevant dataset were used to classify the land use/land cover in Beijing. Through the comparison of the results before and after the year, the changes of land use/land cover before and after the water supply of the South-to-North Water Transfer Project in Beijing were analyzed to supplement the statistical data.The results show that in the first 4 years (2015-2018) in operation of the first phase of middle route of the South-to-North Water Transfer Project, the growth of the value of ecological services of Beijing City is 18.19 billion RMB, of which 6.73 billion RMB is due to the first phase of the middle route of the South-to-North Water Transfer Project. Among them, the ecological service value generated by the new water area are the largest, accounting for 55.02%. The ecological service value generated by pressure mining of groundwater ranks the second, accounting for 34.87%, and the ecological service value generated by the new forest land and the new green land account for 6.90% and 3.21%, respectively. Since the South-to-North Water Transfer did not directly supply wetlands, it is believed that the South-to-North Water Transfer Project had no direct or indirect contribution to the growth of wetland ecosystem service value in Beijing from 2015 to 2018.This research can provide support for the formulation of policies and measures for ecological water use, ecological environment restoration and protection, and efficient utilization of water resources in Beijing and other water reception areas of the South-to-North Water Transfer Project.