Combined with the ground-based GPS-MET observation data and the HYSPLIT trajectory model based on the Lagrange method, the large-scale water vapor transport, convergence characteristics and water vapor source during a persistent heavy rainstorm event on the Northern Slope of the Middle Kunlun Mountains were analyzed. The relationship between large-scale circulation anomaly and water vapor continuous relay transport during heavy rainfall in arid area was clarified. The result showed：(1) Before the precipitation, the location of 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 stretched to the northwest, and the water vapor from low latitude was conveyed to heavy rainfall area along the Indian summer monsoon circulation and Tibet plateau, gather with the south airflow in front of Tashkent low vortex,which constituted the water vapor transport channel for this heavy rainstorm, and resulted two sharply humidification over heavy rainstorm station. The peak PWV of the station is nearly two times of the climatic average. (2) the temperature anomaly at 300 hPa played an important role in the water vapor transport for this heavy rainstorm. Before and during heavy rainstorm, 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 the anticyclonic circulation at 500 hPa, the warm and wet air was transported northward along the positive windward anomaly center at the low latitude, and converged with the southerly air from the east of the cyclonic circulation in the rainstorm area, providing abundant water vapor supply for the persistent rainstorm.