Abstract: Based on the observation data of rainfall, wind direction and wind speed from national meteorological stations and regional automatic stations, combined with ERA5 and GDAS1 reanalysis data, the circulation background and water vapor transport characteristics of an extreme heavy rainfall at a single station in Hekou on June 14, 2022 were analyzed. The results showed that before the heavy rainfall, the South Asia High weakened and moved southwestward, the Subtropical High weakened and retreated eastward, and cold air in front of the mid-high latitude trough moved southward. The rainstorm occurred near the surface front and the 850 hPa shear line. The high value areas of specific humidity at 850 hPa and 925 hPa were good indicators of the heavy rainfall areas, and the period when the southeast wind speed on the ground increased significantly corresponded to the period of heavy rainfall. The water vapor in the heavy rainfall areas mainly came from the Arabian Sea, the Indian Ocean, and the Bay of Bengal, with a small portion coming from the north and concentrated below 1500 meters. During the precipitation event, the water vapor flux throughout the entire layer was a net inflow, which was concentrated in the lower troposphere. During the strongest rainfall period, the water vapor inflow in the lower troposphere reached its maximum, and the main inflow boundaries of water vapor were the west, south, and east boundaries.