Through sampling and analyzing in 5 typical tributaries of Three Gorges Reservoir, parameters of the water quality andmain nutrients were monitored in Mar.,May and Aug. of 2006. The variation of permenganate index of oxygen demand and CODranged from 1.00-2.50mg/L and 6.00-26.5mg/L respectively. Concentration of organic contamination was not discrepancy inupstream and backwater areas. Values of ammonia nitrogen(NH⁺-N),total nitrogen(TN)and total phosphorus(TP) were0.039-0.367mg/I.0.58-1.67mg/L and 0.005-0.133mg/L, respectively. Concentration of NH⁺-N in Aug.was higherthan thoses in Mar. and May, when concentrations of TN and fP were largely exceed the minimum limited value of eutrophic state.The ratio of TN and TP were favored well for algae growth in nearly all tributaries. Chl. a ranged from 0.94-28.9mg/m³.Chl.avalues in backwater areas of tributaries were exceed upstream and the concentration of Chl.a in May was higher than in Mar. andAug.Utilizing the method of modified Carlson trophic state index(TSI _M)has assessed the trophic; states of the studied area. Thevalues of TSI_M ranged from 36.0-64.2,showing that the trophic state of upstream area was oligotropher to mesotropher and thebackwater areas were mesotropher to eutropher. Trophic state of backwater areas were poorer than upstream, and was affected byimpoundment of the Three Gorges Reservoir.There was a significant positive correlation between Chl. a and COD, but Chl.a was not significant correlation with other nutrient factors. After the Three Gorges Reservoir was completed in 2009,eutrophic trend oftributaries in backwater areas would be more serious with the decrease of flow velocity.