In this study, based on the average precipitation of the summer (July-August) and the NCEP/NCAR atmospheric circulation data of four stations (Lhasa, Shigatse, Zedang and Jiangzi) in the middle reaches of the Yarlung Zangbo River in the hinterland of the Tibet Plateau over the past 57 years (1961-2017), synthesis, correlation analysis and other methods are used to analyze the interannual variation characteristics of summer precipitation in the region, along with its possible causes.The results show the following:1) There is no significant linear trend in the summer precipitation in the region during the past 57 years, and the interannual oscillations of the significant period around 3 a are dominant.2) The interannual variation of summer precipitation in the region is directly related to the amount of the water vapor budget in the region.The anomalous anti-cyclonic water vapor flux transport in the Indian Peninsula-Southeast Asia and the dynamic process of water vapor in the plateau hinterland are the main reasons for the interannual oscillations of midsummer precipitation.3) The troposphere in the bottom of the Indian Peninsula-Southeast Asia anomalous anticyclonic circulation is an important water vapor transport channel for the interannual anomalies of midsummer precipitation in the region.The channel continuously transports water vapor to the plateau in the western Pacific, South China Sea and Bay of Bengal.During this period, large-scale system anomalies, such as the West Pacific subtropical high and the Iranian high pressure, played an important role in the water vapor transport process.At the same time, the plateau and the summer monsoon low pressure and South Asia high pressure provided the dynamic conditions for the water vapor to rise and rise in the plateau hinterland.