Abstract: Combining ground-based GPS-MET observation data with the HYSPLIT_4 trajectory model based on the Lagrange method, this study analyzed the large-scale water vapor transport characteristics and sources during a persistent heavy rainstorm event on the northern slope of the middle Kunlun Mountains. The relation between the large-scale circulation anomaly and water vapor continuous relay transport during heavy rainfall in arid areas was clarified. The results showed that: (1) Before precipitation, the subtropical high was abnormally westward, and the southward airflow on the periphery of the subtropical high caused obvious humidification over the Tibet Plateau. During the heavy rainfall, the subtropical high extended northwest, and water vapor from low latitude was conveyed to heavy rainfall areas along the Indian summer monsoon circulation and Tibet Plateau. This water vapor converged with the southern airflow in front of the Tashkent low vortex, which constituted the water vapor transport channel for this heavy rainstorm. This mechanism resulted in two rapid humidification events over the heavy rainstorm station. The peak precipitable water vapor levels of the station were nearly two times the climatic average. (2) Temperature anomalies at 300 hPa played an important role in the water vapor transport during the heavy rainstorm. Before and during the event, the 300-hPa warm anomaly center excited the 200-hPa anticyclonic circulation anomaly center and meridional wind positive anomaly center. Meanwhile, the 500-hPa anticyclonic circulation anomaly center and cyclonic circulation anomaly center were excited in the south and west of the warm anomaly center (north of the Indian Peninsula). At the back of anticyclonic circulation at 500 hPa, warm and wet air was transported northward along the positive windward anomaly center at low altitudes. This air then converged with southern airflows from the east of cyclonic circulation in the rainstorm area, providing an abundant water vapor supply for persistent rainstorms.