Abstract: Basing on the ERA5 hourly reanalysis data, the spatio-temporal variation and the associated regimes of total column water vapor and water vapor flux over the Three Rivers Source (TRS) region during 1981~2019 are analyzed. The results indicated that the water vapor transport had a large spatial differences and the total column water vapor and water vapor flux decreased from southeast to northwest. A distinct inconsistency was revealed for water vapor transport in July ,corresponding to the average total water vapor in the two high value centers of Hoh Xil and the source region of the Yellow River,and the average water vapor flux was just two low value areas.Meanwhile, two convergence regions were formed in Qumalai, Qingshuihe and Jiuzhi. In recent 39 years, the meridional transports of the mean total column water vapor and water vapor flux showed an increasing trend, while the significant decrease of the zonal transport of the mean water vapor flux in summer caused the decrease of the annual mean water vapor flux. The annual cycle of mean total column water vapor and water vapor flux showed single and double peak respectively. The weakening of the westerly circulation and the enhancement of the Plateau Summer Monsoon and the South China Sea Summer Monsoon may contribute to the increase of total column water vapor and meridional transport, while the plateau thermal effect in summer had a certain disturbance on the meridional transport of water vapor.