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The droughts normally lead to devastating and long-lasting damage to agriculture, economy, and ecosystem, especially in Tibet Autonomous Region (hereafter Tibet) where ecosystem is fragile as a result of its special topographic, geomorphic, and climatic conditions. Due to limited observational data in this region, how often and where these droughts occur is not well understood. In this study, droughts intensity and frequency, as well as dryness condition over Tibet were assessed by using the Standardized Precipitation Evapotranspiration Index (SPEI) with meteorological data from 38 stations during period of 1971-2014. Temperature Vegetation Dryness Index (TVDI) was used to compared with SPEI based on observed drought area of Tibet. Moreover, the dryness condition was explained by the contribution of meteorological factors according to the method of contribution rate. Results indicated that dryness conditions were aggravating during the period 1971-2014 across Tibet. Besides, drought intensity and frequency presented considerable decadal variation over the past 44years with more frequent moderate and severe drought occurring in period of 1981-1990 and 2001-2014 compared with other periods. This highlighted that Tibet has gone through serious drying in the 1970s and since 2000. Factor analysis indicated that precipitation played the most important role in the variation of SPEI-12M. Both drought indexes could effectively detect drought events over Tibet from 2001 to 2014. Investigating and evaluating drought characteristic, causes and drought indexes effectiveness provide essential information for balanced water resource allocation and utilization and drought prevention.