In order to clarify the influence of different terrain on the stable isotope of precipitation in the southwest and the geographical boundary of each water vapor mass, a total of 10 research sites in Sichuan Basin, YunnanGuizhou Plateau, the eastern of QinghaiTibet Plateau and Hengduan Mountains were selected as the study area, analyzing the spatiotemporal variations of δD and δ18O in precipitation in southwest China and initially establishing three regional meteoric water line. Relations between δ18O in precipitation and air temperature, amount and moisture sources were discussed, and HYSPLIT4.9 model was used to analyze and trace water source and migration path of precipitation events in summer and winter half year. The results show that there are significant elevation effects of precipitation stable isotopes in the southwest region, that as δ18O=-0.002 8H-3.93 and R=0.89, values of δ18O and δD in the precipitation are gradually depleted from the Sichuan Basin, the YunnanGuizhou Plateau, the eastern part of the QinghaiTibet Plateau and the Hengduan Mountains, and that the seasonal variation characteristics of the winter half year are positive on a whole, while those of the summer half year are overall negative. In addition to Kunming and Chengdu area, the value of d in the southwest region shows the trend of being low in summer and being high in winter, which is in line with the characteristics of the region influenced by monsoon precipitation in China. Compared with the global meteoric water line(GMWL), slopes and intercepts of regional atmospheric precipitation lines(LMWL) in the Sichuan Basin, the eastern QinghaiTibet Plateau and the Hengduan Mountains are apparently smaller, while those in the YunnanGuizhou Plateau are larger, which is mainly relative with temperature of water vapor condensation and evaporation, water vapor sources and transmission ways. Temperature effect and precipitation effect are different in different regions—there is no temperature effect in the Sichuan Basin, the YunnanGuizhou Plateau, the eastern QinghaiXizang Plateau and the Hengduan Mountains, but a remarkable precipitation effect. There are also differences in dominant water vapor mass in different regions of Southwest China. Based on the preliminary analysis of the dominant water vapor during winter and summer monsoon season in different regions, conclusions can be draw that the areas affected by single water vapor mass are mainly distributed in the southwest and northeast, while the regions influenced by multiple water vapor mass are primarily distributed in the northeast and southeast, that the GuiyangAnshun line is on the border of the Western Pacific water vapor mass and the Bay of Bengal water vapor mass, and that ChengduWolongHuanglong line is on the border of the Western Pacific water vapor mass and the Westerly water vapor.

Key words：atmospheric precipitation; stable isotope; water vapor source; different terrain; southwest region