Through sampling and analysis of 6 horizontal stations and 4 vertical stations in the Three Gorges area, the spatial variation of water quality parameter, dissolved oxygen ( DO), biochemical oxygen demand ( BOD₅ ) and permenganate index of oxygen demand ( CODM.) were revealed in Feb., May and Aug., 2004.Concentration of BOD₅ were retained low level which preceded surface water standard I and COD_Mn changed from Ⅱ- Ⅳ in diverse season.The variation of BOD₅ and COD_Mn ranged from 0.1- 1.3 mg/L and 1.8- 6.3 mg/L respectively.Horizontal concentration of DO, BOD₅ and COD_Mn.in reservoir area were lower than upstream area.In flood season, coneentration of COD_Mn were higher than normal and dry season.In reservoir area, the lower concentration of BOD₅ were due to long retension time and COD due to particulate deposition.The vertical variation of BOD₅ and COD_Mn were not notable and organic pollutant were not layered.Particle COD_Mn rate in total COD_Mn in dry, normal and flood season ranged from 5.5%-27.3%, 9.1%-28.8% and 48.6%-78.3% respectively.Water quality was improved when passing through reservoir.Flux of COD_Mn and BOD₅ decreased 44% and 76% in dry season, 13.5% and 32% in normal season, 31.8% and 19.1% in flood season respectively.There was significant correlation between organic pollutant load and water discharge.Because of algae growth, the saturated rate of DO in Daning river bay is higher than in the main stream of reservoir.