Abstract: Based on conventional observation data, regional automatic station data, NCEP/NCAR 6-hourly reanalysis data, the circulation pattern and water vapor transport characteristics of a persistent rainstorm in Liuzhou from June 28 to July 4, 2021 are analyzed. The results show that: The confrontation between the southern branch trough at 500 hPa and the subtropical high made the vortex shear at 850 hPa become stable and less dynamic, thus establishing a stable and sustainable water vapor channel for the rainstorm area. The outbreak of the South China Sea summer monsoon provided a continuous stream of water vapor for the rainstorm area, and the maximum value belt of water vapor transport was mainly below 700 hPa, with the water vapor convergence in the boundary layer being the strongest at 925 hPa. In terms of water vapor budget, the southern boundary was the main input boundary of water vapor, while the eastern boundary was the main output boundary of water vapor, and the higher the water vapor flowed, the more obvious it was. The contribution of water vapor inflow at the southern boundary to the regional water vapor inflow was mainly below 700 hPa, and the contribution became more obvious at the southern boundary at the lower layer; The Yuanbao Mountain in the north of Liuzhou blocked the water vapor outflow, therefore, the water vapor outflow at the northern boundary below 925 hPa was one order of magnitude less than the water vapor inflow at the southern side.