Abstract: By using Penman-Monteith formula and GIS technology, the authors calculated the evapotranspiration and analyzed the temporal-spatial characteristics of reference evapotranspiration in Northeast China during 1991～2000. The results show that the average evapotranspiration from May to September is increasing annually at the speed of 0.04 mm, especially the speed of Northeast plain exceeds 0.05 mm and the annual increasing area of region whose daily evapotranspirations is not less than 0.4 mm being 2.4873 million hm². The daily evapotranspirations of May and August decrease and the daily evapotranspirations of June, July and September increase. The route of daily evapotranspiration change is from Sanjiang plain to Liaohe plain, and shows a shrinking trend. The gravity centers of daily evapotranspiration exceeding 0.4mm from May to September lie in Hulunbeier plateau and Xiliaohe Plain, the track of gravity centers transfer is from North-West to North-East then to South-West.