Abstract: The variations of stable isotope in precipitation along three vapor transport path are analyzed and compared.Along the south vapor path that is from the equatorial areas through the southwest vapor passage in the Yunnan-Guizhou Plateau towards to the mid-lower reaches of the Yangtze River, the seasonal differences of mean δ¹⁸O in precipitation are small in the sampling stations located in low latitudes, but increase from Bangkok toward north.The δ¹⁸O values in precipitation fluctuate on the whole, showing the different vapor origins.The appearance of the minimum δ¹⁸O at Kunming is related to its high altitude.Along the north vapor path from west to east under westerlies, the seasonal differences of the mean δ¹⁸O in precipitation, between the warm and the cold half-year, are all greater than zero for the stations in the west of Zhengzhou, and then decrease with the increasing longitude.During the cold half-year, the mean δ¹⁸O in precipitation reaches its minimum in Urumqi with the minimum temperature, influenced by the wide Cold-High Pressure over the Mongolia, then increases with longitude gradually and keeps at a roughly same level from Zhengzhou towards east.However, the δ¹⁸O values in precipitation are lower in the east than in the west during the warm half-year, influenced by the summer monsoon o-ver East Asia markedly.Along the plateau path that is from the tropics through the Indian Subcontinent and the Himalayas to the northern Tibetan Plateau, the mean δ¹⁸O values in precipitation are correspondingly high in the south parts of the India Subcontinent, and then decrease with latitude gradually.A sharp depletion of the stable isotopic compositions in precipitation takes place due to the very strong rainout of the stable isotopic compositions in vapor in the process of the lifting on the southern slope of the Himalayas.The δ¹⁸O in precipitation is kept at a low level from Nyalam to the Tanggula Mountains during the rainy season all the while, but increases with increasing latitude persistently from the Tanggula Mountains to the northern Tibetan Plateau because of the replenishment of vapor with the relative heavy stable isotopic compositions originating from the inner Plateau.The situation in the dry season is different: the mean δ¹⁸O values in precipitation decrease basically along the path from south to north.Generally, the mean δ¹⁸O in precipitation during the rainy season are lower than in the dry season for the regions controlled by the monsoons over South Asia or the Plateau, but contrary for the regions without monsoon or by weak monsoon.