Abstract: As the core foundation of water ecological environment management,the scientific rigor and refinement of water quality standards directly determine the effectiveness of water ecological conservation.Given the deficiencies of China's current water quality standards in terms of ecological relevance and spatially differentiated management,this study systematically analyzes the differentiated water quality standard system centered on "designated uses" under the U.S.Clean Water Act (CWA).It conducts an in-depth analysis of the U.S.two-tier management structure of "federal benchmark guidance+state standard implementation",clarifies the logic behind ecoregion-based nutrient criteria development,and explains the significance of anti-degradation policies.By drawing on typical case studies(including the refined use designation in Alaska and the Biological Condition Gradient model in Minnesota),this research reveals their practical experience and pivotal implications for indicator formulation and impaired water body identification in water quality standards.In response to China's paradigm shift in water environmental management from "pollution control" to "ecological health" and addressing existing management bottlenecks,specific recommendations are put forward,including refining the classification of water body uses,establishing a differentiated threshold system based on ecological ecoregion,water body classification and condition gradation,and incorporating biological integrity indicators into compliance assessment for water quality attainment.Ultimately,this study aims to provide a theoretical basis and pathway reference for advancing the refined management of China's water ecological environment.