GPS technologies show many capabilities for monitoring atmospheric water vapor. This study uses GPS data from the Japan International Co-operation Agency (JICA) and Hubei GPS network to monitor precipitable water (PW) over the Qinghai-Tibet Plateau (QTP) and over the middle Yangtze River Valley (YRV). The results show that the southern QTP is wetter than the central area due to the barring effect of the Plateau on the monsoon. PW is higher in summer than other months over either the QTP or the middle YRV. The diurnal variation of PW over the QTP is more complex than that of the middle YRV with fluctuations occurring during the whole day due to the unique topography. The minimum PW over both the QTP and the middle YRV appears in the morning; however, the peak over the QTP occurs at night while the peak over the middle YRV occurs in the early afternoon. Furthermore, PW over the QTP, especially its southern and eastern edges, are positively correlated with PW over the middle YRV. This may imply that the southern and eastern Plateaus are key regions transporting atmospheric vapor to the middle YRV. Our results indicate the possibility of finding early warning signals resulting from the intensification of the QTP atmospheric vapor leading to heavy rainfall events over the middle YRV.