Abstract: The authors have quantitatively estimated the time scale of the geomorphologic response of the Yarlung Zangbo Grand Canyon, correlated the features of the Grand Canyon and the river courses of its upper reaches and performed sediment analysis and dating of terraces at the entrance of the Grand Canyon. On that basis, combined with the recent progress in tectonic study and numerical analysis of geomorphologic features, the authors have demonstrated systematically the formation of the Yarlung Zangbo Grand Canyon. The study shows that the present-day Yarlung Zangbo Grand Canyon and the river courses in its upper reaches belonged to two different river systems before the formation of the Grand Canyon. About 30 ka BP, the Za Qu-Zhibai River—a tributary of the Parlung Zangbo system—captured the paleo-Yarlung Zangbo (which is presently located in the upper reaches of the Zhibai River) due to head erosion; as a result, the paleo-Yarlung Zangbo River, which originally flowed southward through the Nanyi valley (Nayipu Qu) out of the ancient highland, joined the Parlung Zangbo and then the Yarlung Zangbo Grand Canyon came to being and eroded downward intensely, thus forming the drainage structure of the present famous Grand Canyon and big bend.