Abstract: Based on the conventional meteorological observation data, the ERA-interim reanalysis data from the ECMWF and NCAR/ NCEP reanalysis data, we have conducted analysis of the large-scale circulation of a sustained heavy rain event in Hunan in early July 2019, with focus on the transport and budget characteristics of water vapor in the different periods of this event by using the trajectory model HYSPLIT4. The results show that(1)this event, which lasted for 4 days, can be divided into three periods. Precipitation in the first period is generated by a cold shear line, which occurs in the warm sector in the second period, and is caused by a cold front in the third period. (2)In the different periods of this event, the paths of water vapor transport and their proportion and height in the different paths are different. In the first period, the water vapor from the Bay of Bengal and the inland areas of high latitudes account for 3/4 and 1/4 of the total, respectively. All the water vapor in the second period are from the tropical ocean surface of the Bay of Bengal and the South China Sea in the low-latitudes.Most of the water vapor in the third period are from the Bay of Bengal, and 10 percent of them are from the eastern coast of China and are transported by the northeast Hunan to the heavy rain areas due to the influence of cold air.(3)Most of the water vapor required to sustain the heavy rain event is imported from the southern and western boundaries to the heavy rain areas and converges in the low-level, and then is transported by ascending motion to the upper-level, resulting in heavy precipitation.