Backward tracking and quantitative analysis of water vapor transport at different altitudes during rainstorms on the eastern, western, and east-west feet of Helan Mountains from 2001 to 2019 are conducted by the Hybrid Single Particle Lagrangian Integrated Trajectory Model (HYSPLIT), based on hourly precipitation observations and GDAS reanalysis data with a spatial resolution of 1.0°×1.0° and a temporal resolution of 6 hours. It is found that significant differences exist in water vapor transport patterns at different altitudes during rainstorms across different regions of Helan Mountains. At the eastern foot, the southerly path is identified as the primary transport route below 3000 m, with a water vapor contribution rate of 57.3% to 75.2%. The contribution of the westerly path is observed to increase with altitude, reaching 100% at the 5000 m height. At the western foot, the westerly path is found to be the dominant transport route, with a water vapor contribution rate ranging from 31.8% to 67.5%. The southerly path is the secondary, with the contribution rate ranging from 23.8% to 68.2%, while the northerly path appears only at the heights of 100 m and 1000 m, contributing 28.9% to 39.4%. In the east-west foot region, the westerly path is determined to contribute 100% of the water vapor at all altitudes. The Eurasian westerlies are identified as the predominant source of water vapor, particularly during rainstorms in the east-west foot region, where the water vapor contribution is the highest at all altitudes except at the 1000 m height. Secondary water vapor sources include the Qinghai and Gansu regions, the middle and lower reaches of Yangtze River, and the waters of the Black Sea, Caspian Sea, Lake Balkhash, and Lake Baikal, which are found to supply moisture to rainstorms at the east-west, eastern, and western feet, respectively. The Hengduan Mountains are identified as contributing moisture at isolated altitudes during rainstorms at the eastern and western feet, and its contribution was minimal.