Abstract: Abundant water vapor supply is a necessary condition for the occurrence and maintenance of rainstorms. The west of Hexi Corridor is located in the deep arid area in the northwest inland of China, but extreme weather events have occurred frequently in recent years. In order to reveal the characteristics and sources of water vapor transport during extreme rainstorms in this region, this paper uses the precipitation data of meteorological observation stations, ERA5 reanalysis data and GDAS (global data assurance system) data to compare and analyze the circulation situation, water vapor transport and budget characteristics of four extreme rainstorms in the west of Hexi, and uses HYSPLIT method to simulate and calculate the water vapor trajectory of rainstorms and the contribution of water vapor from different sources. The results are as follows. (1) There are two types of circulation patterns during the four extreme rainstorms. The 500 hPa height field of the "low vortex type" rainstorm is high in the east and low in the west, and the low vortex in the north of the Qinghai Tibet Plateau is the main influence system. The 500 hPa height field of the "subtropical high marginal type " rainstorm is high in the south and low in the north, and the Western Pacific subtropical high is the main influence system. (2) The two types of rainstorms have west and south water vapor transport belts. The water vapor source of the west transport belt is the same, but the south transport belt is different. In the "low vortex type" rainstorm, the west of the lower layer has strong water vapor transport intensity, and the middle layer is dominated by the south. In the "subtropical high marginal type" rainstorm, the south of the lower layer has strong water vapor transport intensity, and the middle layer is dominated by the west. (3) In the two types of rainstorms, the proportion of the net input of water vapor in the lower layer to the net input of the whole layer is more than 60%. In the "low vortex type" rainstorm, the water vapor input is mainly the west and north boundaries of the low layer and the east boundary of the middle layer. In the "subtropical high marginal type" rainstorm, the water vapor input is mainly the east boundary of the low layer and the west boundary of the high layer. (4) The water vapor sources of "low vortex type" rainstorm at 500 hPa are mainly the northern Xinjiang, the east of Southwest and the Mediterranean sea (Black Sea), while water vapor sources of at 700 hPa are mainly in Central Asia (Caspian Sea) and the east of Southwest. The water vapor sources of the "subtropical high marginal type" rainstorm at 500 hPa are mainly from the Mediterranean sea, while water vapor sources at 700 hPa are mainly from South Asia and western South China. The three-dimensional structure models of water vapor sources and paths of two types of extreme rainstorms in the west of Hexi were established, and the sources and contribution rates of water vapor in each layer were determined. The results will help to understand the formation mechanism of extreme rainstorm in the west of Hexi, and provide some reference for the rainstorm forecast in this area in the future.