In order to scientifically identify and evaluate the impact of the Western Route of the South-to-North Water Diversion Project (Phase Ⅰ) on the hydrology and water resources, ecological environment, and social economy of water source areas, the comprehensive situation of the project-affected water source areas was considered. In addition, based on literature and normative standards, a comprehensive impact assessment system for the Western Route of the South-to-North Water Diversion Project (Phase Ⅰ) was established, covering multiple criterion levels including hydrology and water resources, ecological environment, water energy utilization, and social economy. Moreover, the weights of the evaluation indicators were determined by the subjective and objective comprehensive weight method based on the fuzzy analytic hierarchy process and the improved entropy weight method. Combined with the TOPSIS method, the comprehensive situation of the water source areas along the Western Route of the South-to-North Water Diversion Project (Phase Ⅰ) from 2012 to 2021 was objectively evaluated. The results indicate that the comprehensive situation of the water source areas along the Western Route of the South-to-North Water Diversion Project (Phase Ⅰ) has improved, transitioning from a poor state prior to 2017 to a healthier one by 2021.