The Yarlung Zangbo River is a great river in the Tibetan Plateau, and the landform of river valley and geological evolution history of its development has an important significance for the study of the Tibetan Plateau geology. Previous researchers tested lacustrine sediments by ESR and 14 C methods in the Yarlung Zangbo River valley and recognized four periods of dammed lakes. The authors analyzed lacustrine samples with OSL (Opically Stimulated Luminescence) and got the ages of (50.9± 2.1) ka BP and (1.8 ±0.1) ka BP. These data suggest that the Yarlung Zangbo Great Bend had two ancient dammed lakes existent respectively during the early stage of the last glacial period and the new glacial period.