It is indispensable to explore the spatiotemporal variation of reference evapotranspiration over the Tibetan Plateau and its driving factors so as to deepen the understanding of regional hydrological process and its response to climate change. The daily data from 75 meteorological stations over the plateau were utilized to analyze the spatiotemporal change of evapotranspiration based on the modified formula of FAO 56 Penman-Monteith,and the contribution of climatic factors to the variation during the period of 1971 - 2014 was discussed. The main conclusions are summarized as follows: Annual reference evapotranspiration over the Tibetan Plateau tended to an increase,especially in the region south from 33°N from 1997 to 2014 with an average linear trend of 40.16 mm·(10a) ~(- 1). It, however,decreased remarkably at the rate of - 27.07 mm·(10a) ~(- 1) from 1971 to 1996,and the dominant climatic factor resulting in the decrease was the reduction of wind speed,especially in Northern Plateau. Reduction of relative humidity played a crucial role in increasing the reference evapotranspiration from 1997 to 2014. In addition, the biggest contribution factor to the seasonal variation of reference evapotranspiration shifted from the reduction of wind speed (from 1971 to 1996) to the decrease of relative humidity (from 1997 to 2014) and the dominant factor to the summer variation of reference evapotranspiration shifted from the increase of relative humidity (from 1971 to 1996) to the increase of annual mean relative sunshine duration (from 1997 to 2014).