Abstract: The Tibetan Plateau is one of the ideal areas of the world to investigate evapotranspiration because of the minor impact by humans. But the investigation has been insufficient for owing to the lack of sufficient observational data. Based on the data from the Intensive Observation Period (IOP) of the GEWEX Asian Monsoon Experiment (GAME) in the Tibetan Plateau in 1998 and the meteorological observatories during the period 1967 to 2006, this paper presents on analysis of the reference evapotranspiration, potential evapotranspiration and actual evapotranspiration. The result indicated that reference evapotranspiration decreased during the period 1967 to 2006, but obviously higher than the 40-year average from 1967 to 2006. Furthermore, there was a very high correlation (n=72, r²=0.97) exist between reference evapotranspiration and potential evapotranspiration. The air temperature, net total radiation, wind speed and vapor pressure deficit were also higher than the 40-year average during the GAME-Tibet IOP. The analysis showed that the increased of reference evapotranspiration was due to the increased of net total radiation, wind speed and vapor pressure deficit, and regarded the latter two as the major impacts (n=72, P<0.05). During the GAME-Tibet IOP, actual evapotranspiration of 10-day average fluctuated between 9 mm and 23 mm. Form June to August, the total actual evapotranspiration could achieve 123.3~136.9 mm, which was 38.2%~73.4% of the precipitation in the same period. These all clearly show that evapotranspiration has played an important role in the Geo-gas interaction of the Tibetan Plateau.