Abstract: Using HYSPLIT and GDAS, it will be analyzed what is the water vapor contribution of the 16 rainstorms, and what includes backward water vapor trajectory tracking, main channels and different sources in the warm season of 1981-2020 in western southern Xinjiang (April-September). the result shows: Water vapor mainly originates from Southwest Asia, Central Asia, the Mediterranean Sea and the Black Sea and their vicinity, the Atlantic Ocean and its coasts, at 850 hPa in the plain area, there is water vapor originating from southern and northern Xinjiang. At 500 hPa, water vapor mainly enters the rainstorm area from the west channel, the contribution of water vapor to the heavy rain is greater and the loss is also greater, that comes from Southwest Asia and Central Asia. In the lower troposphere, there are two main channels for water vapor to enter the rainstorm area from the west and east. At 700 hPa, the contribution of each channel and each water vapor source to the rainstorm is different in different regions. In the plain area of 850 hPa, the eastward channel of the heavy rain contributed the most to the heavy rain, and the water vapor loss along the source area was small, and the largest contribution to the heavy rain was in the source area of northern Xinjiang. In the plain area, water vapor originates from Southwest Asia, Central Asia, Southern Xinjiang and Northern Xinjiang. It is mainly transported to 700 hPa and below. It originates from the water vapor near the Mediterranean Sea and the Black Sea, the Atlantic Ocean and its coast, it is mainly transported to a height above 700 hPa. At 500 hPa in the plain area, the water vapor transport of heavy rain is dominant from more than 2000 m, while the mountainous area is the opposite. In the western part of southern Xinjiang, there are sources of water vapor from southern and northern Xinjiang during heavy rains, and under certain conditions, there are sources of water vapor from North America and North Africa, which are different from previous research results.