The variation characteristics of reference crop evapotranspiration(ET_0)and its sensitivity to main meteorological factors in Xingan League of Inner Mongolia under the background of climate warming were studied.ET_0 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 Xingan League.Then the spatial-tempral variation characteristics of ET_0 over Xingan League were analyzed with the help of the methods of linear regression and accumulative anomaly.In addition,sensitivity of ET_0 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 didnt passed the significant test.(2)In the past 45 years,the averge ET_0 of Xingan 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 ET_0 in growing season of Xingan League showed an increasing trend,but the trend of increase was not significant.The variaty of average daily ET_0 in growth season of Xingan League during 1973-2017 can be roughly divided into five distinct stages.(3)In the past 45 years,the average daily ET_0 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)ET_0 is positively sensitive to temperature,average wind speed and sunshine hours in growing season of Xingan 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 ET_0 to temperature,sunshine hours and average vapor pressure were mainly distributed in eastern and southern of Xingan League.The northern part and southeast corner were sensitive areas of ET_0 to the average wind speed.