Since the Quaternary, many lakes have been present in the Qinghai-Tibetan Plateau. As peculiar geological processes in the evolution of the uplifting of Qinghai-Tibetan Plateau, the distributions and evolutions of the Quaternary paleolakes in the Qinghai-Tibetan Plateau have been the focus of interest among the international geosciences circle. Comparisons of the newly obtained and existing data from field surveys, remote sensing images, characteristics of tectonic landforms and distribution of the lacustrine strata, the author have, for the first time, defined a large-sized Quaternary Qiangtang Paleolake. The paleolake starts from the east-westerly direction at Rutog in western Tibet, passing through Gêrzê, and finally ends at Nagqu in eastern Tibet. Its length is approximately 1,200 km; it is about 420 km at its widest point (north-southerly). The Paleolake forms an E-W (or NWW) ellipsoid with an estimated area of 354920 km2. The Paleolake is bordered by the Mts. Gangdisê and Nyainqêntanglha to the south and the Karakorum Pass-Tozê Kangri-Zangbagangri- Tanggula Pass to the north. It generally appears as a basinal landform with low mountains and valleys in the central part (altitudes of 4400 m) and higher altitudes (5000 m) in the peripheries. The formation and development of the Paleolake was controlled by the nearly E-W trending structures.