Abstract: The variety and impact factors of the dissolved oxygen(DO)concentration and saturation at the two sections,up-stream or downstream,of the Three Gorges Project dam after the impoundment are analyzed based on the field data. The results reveal that,since a great deal of oxygen dissolves into water due to the air entrainment when water sluices through the orifices, the phenomenon of DO super-saturation is observed in the downstream of the dam. However,DO concentration(saturation)in the downstream hardly varies if water sluices through the electricity power stations. When water sluices through the electricity power stations and orifices synchronously,DO concentration(saturation)of the downstream is mainly affected by the ratio of the two discharges. Additionally,the downstream water level also has an impact on the downstream DO concentration. When the total discharge is more than 35 000 m³/s and the downstream water level is higher than 68m,or when most of the discharge sluices through the orifices,great attention must be paid to the effect of DO super-saturation on the aquatic.