Under the background of global warming,the change and spatial distribution of reference crop evapotranspiration are bound to have an important impact on agricultural water resources planning and agricultural water management in the main grain producing areas of China.The main grain producing areas of China was divided into temperate humid and semi-humid area (I area),temperate arid and semi-arid area (II area),warm temperate semi-humid area (III area) and subtropical humid area (IV area) according to the difference of heat and humidity.Based on daily meteorological data of the 265 stations in the main grain producing areas of China during 1961 to 2013,the daily ET_0 was calculated by Penman-Monteith equation recommended by Food and Agriculture Organization in 1998.The temporal and spatial variation of ET_0 and its influencing factors were analyzed by using Arcgis spatial interpolation,Mann-Kendall trend test,sensitivity analysis and contribution rate analysis.The results showed that the annual ET_0 in major grain producing areas of China was 878.9mm and had a significant downward trend as a whole at the rate of 0.47mm·y-1(P<0.05) in the past 53 years.The annual ET_0 of I,II and IV area decreased with the value of 741.8mm,1079.8mm and 924.2mm respectively,but the trends of changes were not obvious.The annual ET_0 of III area was 940.2mm,which had an extremely significant downward trend with a rate of 1.21mm·y-1(P<0.01).Sensitivity analysis indicated that relative humidity was the most sensitive meteorological factor to annual ET_0 change in the whole and I-IV area,with the sensitivity coefficient of -1.060,-1.232,-0.784,-1.114 and -1.009,respectively.Contribution analysis showed that wind speed made the greatest contribution to ET_0 changed in I-III and whole area,while relative humidity was the meteorological factor that contributed most to the change of ET_0 in IV area.The decrease of wind speed was the dominant cause of ET_0 decrease in I-III and whole area,and the main reason for the decrease of ET_0 in IV area were the decrease of wind speed and the shortening of sunshine hours.