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This paper mainly analyzed the isotopic effect of precipitation in the Yarlung Zangbo River.On the whole,the isotopic compositions of most water samples fall on the upper fight of the global meteoric water line.According to δD and δ18O data of the samples,the precipitation equation is figured out as δD=8 δ18O+10,showing that they are derived from precipitation but have experienced intensive evaporation.With obvious region-continental effect (a continuous depletion in heavy isotopes in water bodies occurs with increasing distance from the coast),the water presents a reducing trend of δD and δ18O westwards and southwards.Altitudinal effect is evident here,occurring in both trunk stream and main branches of the Yarlung Zangbo River.The distribution of water isotopic compositions is concerned with the movement of precipitation clouds from the Bay of Bengal and the Nujiang River and is affected by the topographic and climatic conditions of the Tibetan Plateau.