The Xizang Plateau, with a common altitude of more than 4000 m sbove sea level,has long been celebrated as “The Roof of the World”. In order to study oxygen isotopic composition of meteoric water in the Xizang Plateau Region and its relationship with the attitude, we made an investigation tour to the Xizang Plateau, starting from Guizhow, during 1979 from July to October, and 79 meteoric Water samples were collected, including brook, well, lake, snow, firn, spring and running waters, at different altitudes. Oxygen isotope analyses indicate that the isotopie composition of meteoric water in the areas more than 4000g and in the western parts of SichuanGaizhow shows remarkable altitude effect. There is a negative correlation between δ28O and altitude, which is reflected by --δ18O = 0.0026H+7.75. The average δ18O value for metcoric water in the areas: more than 4000m above sea level turns out to be --18.15‰ is evident that δ18O value for lake water on the plateau is related to its water supply. δ18O value for lake water, in which the evaporation is greater than supply,is approximately three or four times higher than that of supplied water, averaging -5.74‰. Oxygen isotopic compasition of geothermal water can be compared with that of local meteoric water, but shows certain δ18O-shift, suggesting that the main water-supply source seems to be meteoric water in the same area.
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