Abstract: Using SST (sea surface temperature) data from the Hadley Center, ERA-Interim reanalysis data, and OLR data from NOAA, the relationship between the summer water vapor content over the Tibetan Plateau moist pool and the preceding SST anomalies in the Indian Ocean during 1979-2011 and its possible reasons are studied. The results show that the second leading EOF mode of the detrended water vapor content in summer over the Tibetan Plateau moist pool is positively related to SST anomalies over the key area (5°S-20°N, 45°E-75°E) in March and April, thus SST over this key area can be regarded as a precursor of the summer water vapor content. In warm years, the significant easterly anomalies near the equator play a crucial role in the transport of water vapor. The subtropical high in the western Pacific strengthens and moves westward at 500 hPa. At 600 hPa, the significant easterly anomalies are favorable for water vapor transport from the western Pacific, the South China Sea and the Bay of Bengal to India. Under the influence of southerly winds on the western flank of the anticyclone, large amounts of water vapor are transported to the Tibetan Plateau. There is divergence over the Tibetan Plateau and convergence over the western Pacific in the upper troposphere. The above anomalous circulation indicates that the summer water vapor content is much higher over the Tibetan Plateau moist pool in warm years than in cold years, and vice versa. As far as the mechanism is concerned, the significant warm SST anomalies in Indian Ocean can induce anomalous convective updrafts at the springtime, and the anomalous Walker circulation can maintain from the spring to summer. As the WPSH (western Pacific subtropical high) moves northward seasonally with anomalous intensification and westward expansion, equatorial easterly anomalies enhance and move westward as well, which eventually bring more water vapor to the Tibetan Plateau through the above transport path.