Abstract：Based on the 1∶100,000 and 1∶500,000 topography maps, the authors investigated rivers (hydrology), snow lines, glacier heights and relationships of the lake area and mountain area at different heights in mountain lake basins on the Qinghai-Tibet Plateau. The area of plateau lakes is closely related with that of their catchment mountains (the elevations are >500-750 m above the present lake level in the central and western parts of the plateau and >250 m above the lake level in the eastern part of the plateau). These suggest that mountain precipitation is probably the main source of lake water and that its quality (low temperature) and quantity are the main factors for maintaining the size and stability of the lakes. Owing to these special hydrological characteristics, the mountain lakes on the plateau expanded more significantly than lowland and hill lakes during the warm-wet period in the geologic past. At 40-23 ka BP, the mountain lakes on the plateau underwent unusual expansion, which was probably because more moisture was transported to the mountainous areas and more low-temperature water flowed to and stored in the mountain lakes during the increase of monsoonal rain in the warm period.