Abstract: Based on the meteorological observation data collected by the 38 weather stations in Tibet for several decades before 2006, the daily values of the reference crop evapotranspiration (ET₀) are calculated by FAO-56 standard Penman-Monteith formula, and the daily and monthly change law of ET₀ over the seven stations is analyzed. The tendency test is conducted on the data of the monthly and annual ET₀ using the Mann-Kendall method. The contour maps of the average annual ET₀ in Tibet are obtained using the Golden Software Surfer 8.0. The spatial distribution of the average annual ET₀ in Tibet is analyzed with the function of spatial analysis. The results indicate that:the daily ET₀ curves of Changdou, Linzhi and Naqu are approximately the same, showing a single peak parabolic shape; and the daily ET₀ curves of Lhasa, Rikaze and Zedang are also approximately the same. The curves from June to September quickly take on the downward trend; ET₀ of the Shiquanhe presents individual change trend. As for all the observation sites, the maximum monthly ET₀ is found in June,and the minimum is in December. In Rikaze, ET₀ mainly shows the decreasing trend each month and in wet and dry seasons very significantly, followed by Zedang. While ET₀ mainly shows the increasing trend in Linzhi. The Mann-Kendall test also indicates that the decreasing in annual ET₀ appears to be the dominate trend in most stations of Tibet. The spatial distribution of average annual ET₀ reveals that the ET₀ values are higher in the eastern and central-southern regions than those in the west and north as well as in the south-eastern fringe in Tibet.