Abstract: Based on the daily meteorological measurements of 106 meteorological stations in Northeast China from 1951 to 2007,the daily reference evapotran spiration (ET₀) and yearly ET₀ are estmiated using the Penman-Monteith equation1 Gridded annual and annual-average ET₀ values for the region are produced using the inverse distance weighted interpolation method.The spatiotemporal variability of ET₀ is analyzed using the methods of Mexican hat wavelet transform,Mann-Kendall test,the rotated empirical orthogonal function,and the inclination rate.The results show that:(1) a slightly increasing trend (3.89 mm/10a) is detected in the regional-average ET₀ tmie series,and the regional ET₀ minmium and maxmium are found in 1953 and 1982,respectively; (2) the temporal variability of regional-average ET₀ has a quasi-periodicity of 8216 years experiencing four alternating stages (low-high-low-high),and in which an intensified ET₀ oscillation of 8210 years is observed; (3) the annual-average ET₀ ranges from 600 mm to 1.60 mm,and appears as obviously spatial difference exhibiting semiring-shaped isogramswith a gradual ET₀ increment from Northeast to Southwest; and (4) the annual-average ET₀ shows a increase trend over 72161% of the region doma in based on the analysis of inclination rate,while the opposite result is obtained for the rest of the region; the maxmium and minmium values of inclination rate are 3016 mm/10a at Nenjiang station and 224.4 mm/10a at Yebaishou station,respectively.