Based on the ERA-Interim monthly mean reanalysis data from 1979 to 2016， the climate variation characteristics and causes of water vapor budget over the Tibetan Plateau are further researched by means of statistical analysis and diagnostic method. The results show that the annual and seasonal average water vapor flows in the Tibetan Plateau via the southern， western and northern boundaries， while it flows out via the eastern boundary. The Tibetan Plateau is a significant water vapor sink in spring， summer and autumn， while water vapor is exported from the plateau in winter. Summer is the most active season for water vapor transport over the plateau. The water vapor transport and water vapor budget are greater over the eastern （southern） part of the plateau than those over the western （northern） part of the plateau. The Tibetan Plateau has a gradual wetting trend in years and summer， because of the significant reduction of water vapor outflow from the eastern boundary. The net water vapor budgetexhibits an increasing trend over the eastern and the western part of the plateau， and the increasing trend values over the western part of the plateau is larger than those over the eastern part. The decrease of the water vapor outflowing via the eastern boundary is the main reason for the increase of the net water vapor inflow in the eastern part of the plateau， and the obviously increase of the water vapor inflowing via the southern boundary is the main reason for the increase of the net water vapor inflow in the western part of the plateau. The interannual variation of water vapor budget over the northern part of the plateau is more obvious than those over the southern part. There is an obvious humidification trend over the northern part of the plateau， but there is no obvious humidification trend over the southern part. The variation of water vapor budget via the southern boundary over the Tibetan Plateau in summer is mainly affected by the southerly airflow in the monsoon controlled area over the area east and south of the plateau， and is also closely related to the variation of the Western Pacific Subtropical High. The variation of water vapor budget via the western boundary is mainly affected by the water vapor transport in the middle latitude westerly belt. The variation of water vapor budget via the northern boundary is mainly affected by the teleconnection wave train of “the Silk Road”. The less water vapor inflow via the eastern boundary is related to the anticyclone anomaly from the northeast of the plateau to the vicinity of Baikal Lake and the cyclone anomaly over South China. In short， the climate change of the water vapor budget over the Tibetan Plateau has significant regional and local characteristics. Consequently， it is necessary to investigate the climate variation characteristics and causes of water vapor budget over the Tibetan Plateau. The Tibetan Plateau is a special area for responding to climate change. Under global warming， the water vapor transport and water vapor budget in this region will change significantly， which will further result in abnormal changes of rainfall. The research results can further understand the process of water cycle， reveal the mechanism of water vapor budget change over the Tibetan Plateau， and provide a scientific basis for the change of water resources over the Tibetan Plateau. We hope this research can provide a theoretical basis and scientific support for water security and water resources management over the Tibetan Plateau.