COD是我国污染减排工作的重要考核指标之一。如何科学核算COD减排是保障我国国民经济和社会发展规划顺利实施的关键问题之一。论文基于分布式水循环模型，构建了流域COD减排核证评估框架；并以淮河中上游为例，分析了多种减排情景对流域水环境的影响，识别了污染减排任务较为艰巨的地区。研究表明：①基准年（1991—2000 年） 研究区出口断面COD_Mn平均浓度为Ⅳ类水水平。为使出口断面水质达到水功能区标准（Ⅲ类），全流域COD入河点源负荷应削减约18%。②沙颍河中游、涡河上游和贾鲁河、淮河以南等地区水污染状况对减排变化较敏感。若全流域COD入河总负荷削减50%以上，流域水环境质量有明显改善，但北汝河、洪汝河中游、沙颍河下游、涡河上游依然为劣Ⅴ类水体，这一地区农业非点源污染对水污染的贡献比较大。③为改善淮河流域水环境状况，必须加强对入河COD排放的控制，但同时对重点地区农业非点源污染的控制也不可忽视。研究将为流域水污染防治、水质管理提供技术支持和科学指导，也为我国“十二五”节能减排规划的制定和实施提供参考和借鉴。

COD is the most important evaluation index of pollutants discharge reduction in China. How to scientifically account and assess the effects of COD discharge reduction is one of the key problems to guarantee successful implementation of the national economic and social development program. In this study, an assessment framework of COD discharge reduction has been explored based on distributed hydrological model at basin scale. Moreover, the middle and upper reaches of the Huaihe River is selected as study area, and the impact of different reduction scenarios on water environment at some key cross-sections has been analyzed and severe regions of reduction task are identified. The results showed that: 1) the average concentration of COD belonged to Class IV at the outlet of the study area during 1991 and 2000. Nearly 18% of the current COD load should be reduced in order to meet the water quality standard of water function zone (Class Ⅲ) at the outlet section. 2) The most sensitive regions to COD discharge reduction included the middle Shaying River, the upper Guohe River, Jialu River and the south of Huaihe River. The water environment would be significantly improved if the COD load discharged into rivers was reduced by a half. But the water environment was still severe, belonging to Class V in the drainage basins of Beiru River, the middle Hongru River, the downstream of Shaying River and the upstream of Guohe River, where the agricultural non-point source pollution contributed a larger proportion to the water pollution. 3) In order to improve the water environment of the Huaihe River Basin, the control of COD discharge should be paid more attention, and the non-point source pollution prevention in some key regions shouldn't be ignored. The study will be expected to give technical and scientific guide for the water pollution prevention and water quality management, and also provide reference and foundation for the establishment and implementation of energy saving and emission reduction in the 12th Five-Year Plan period.