Abstract: The variation characteristics of reference crop evapotranspiration(ET₀) and its sensitivity to main meteorological factors in Xing'an League of Inner Mongolia under the background of climate warming were studied. ET₀ in growing season during 1973-2017 was calculated by using Penman-Monteith equation recommended by FAO based on daily meteorological data of eight weather stations in Xing'an League. Then the spatial-tempral variation characteristics of ET₀ over Xing'an League were analyzed with the help of the methods of linear regression and accumulative anomaly. In addition, sensitivity of ET₀ to key climate factors, such as temperature, average wind speed, sunshine hours and average vapor pressure was analyzed through using the methods of response curves and sensitivity coefficients. The results show that:(1) Temperature increased significantly(P < 0.01) from 1973 to 2017, while average wind speed showed a decrease trend, sunshine hours and average vapor pressure both showed upward trend, but the variation trend of the latter three factors didn't passed the significant test. (2) In the past 45 years, the averge ET₀ of Xing'an League in growing season is 765.9 mm, the areas of high values were mainly distributed in Tuquan county and the central part of Keyouzhongqi, the areas of low values being mainly distributed in the northwest of Aershan. The average daily ET₀ in growing season of Xing'an League showed an increasing trend, but the trend of increase was not significant. The variaty of average daily ET₀ in growth season of Xing'an League during 1973-2017 can be roughly divided into five distinct stages. (3) In the past 45 years, the average daily ET₀ increased significantly during the growing season of Aershan, Suolun and Bayanhushu(P < 0.05), the variation tendency of Tuquan is not obvious, Indeer and Ulanhot showing a weak downward trend. (4) ET₀ is positively sensitive to temperature, average wind speed and sunshine hours in growing season of Xing'an League only show negative sensitivity to average vapor pressure, which was the most sensitive to temperature followed by the average vapor pressure and the lowest sensitivity to the average wind speed in the meantime.(5) The sensitive areas of ET₀ to temperature, sunshine hours and average vapor pressure were mainly distributed in eastern and southern of Xing'an League. The northern part and southeast corner were sensitive areas of ET₀ to the average wind speed.