Using the observational and JRA-25 reanalysis datasets, three dimensional structure of water vapor transportation and its relationships with the summer flood/drought situations are investigated in summer time over the Huaihe River Basin (HRB) in eastern China. Results show that there exist major net water vapor input from the western and southern boundaries and net water vapor output in the eastern and northern ones. The water vapor transported from the Bay of Bengal and the South China Sea regions are critical to the precipitation in the HRB region. A typical flood has close relationships with positive anomaly of the transported water vapor from the Bay of Bengal. For a typical drought year, water vapor transported from the Bay of Bengal, as well as the South China Sea, are greatly reduced. And the contribution of the South China Sea is relatively large. Water vapor transported by the tropical westerly also plays a key role in the summer precipitation of the HRB area. Results suggested that the region of the southeast of the Tibet Plateau plays a key role as “transfer post”.