Abstract: Using reanalysis data,GDAS and other data,this paper introduces the HYSPLIT model to qualitatively and quantitatively analyze the water vapor transport characteristics of the heavy rain on September 7th to 8th,and simulate the source of water vapor. The results show that: (1) This process is caused by the combined effects of high-altitude low-groove,low-vortex shear,and low-altitude jet,and the strong precipitation occurrence area has a good correspondence with the 850hPa low-vortex location. (2) The water vapor affecting the heavy rainfall mainly comes from the South China Sea,the Bay of Bengal,and the surrounding provinces such as Guizhou and Hunan. Among them,the local water vapor contribution from the surrounding provinces is the largest. The water vapor contribution rate also reached 39%. (3) Three-dimensional space shows that water vapor mainly comes from areas near or below 850hPa height.