Using the NCEP/NCAR reanalysis data (1°×1°) and the daily precipitation data of 15 weather stations and 200 regional automatic stations over the western South Xinjiang (35° to 42°N, 73° to 80°E) in 2013, the source region, transportation, and budget features of the water vapor associated with four typical rainstorm processes over the region are analyzed. The results show that in these processes, where a strong lowlevel easterly jet (LLEJ) played a significant role, the vapor sources mainly were the Arabian Sea and the Bay of Bengal, followed by the Persian Gulf. In Process 1, the vapor was mainly transported via the easterly and southwesterly. The strong convergence over the mountains in the west and the plain in the east of South Xinjiang triggered the rainstorm. The vapor transportation with high value lasted for 24 hours, was lager in the easterly path than the southwesterly one. In Process 2, there were three paths of vapor transportation: westerly, southwesterly, and easterly, which all generated severe convergence over the western South Xinjiang and induced the extensive and strong rainstorm. The vapor input of the easterly boundary was close to that of the southerly one. The vapor transportation of high value lasted for 60 hours. In Process 3, the vapor transportation was along the westerly, southerly and easterly path. The vapor led by LLEJ, under the intersection of the westerly and easterly, heaped up along the mountains, producing the strong convergence and the rainstorm. The vapor transportation of high value lasted for 24 hours. In Process 4, the vapor transportation was mainly along the westerly, southerly, and easterly paths. The vapor input of the westerly was much larger than that of the easterly and southerly. There appeared for 2 times that the highvalue vapor transportation areas of lower and upper levels were superposed, during which the area with highvalue vapor lasted for 48 hours.