Abstract: As a critical hydrometeorological parameter, reference evapotranspiration (ET0) plays an important role in the global ecosystem. In order to deepen the understanding of how ET0 changes in humid regions, we calculated ET0 by using the PenmanMonteith equation and data from 87 meteorological stations in Hunan Province from 1960 to 2015. We applied linear trend, MannKendall test and inverse distance weighting interpolation methods for the analysis of spatiotemporal variations of ET0 and major meteorological variables, and selected the variables involved in the equation to identify the contribution to variability of ET0 using stepwise regression. Results indicated that: (1) average annual ET0 decreased at a rate of -3346 mm per decade. The declining trend of ET0 is mainly explained by the decline in sunshine duration and wind speed. On the contrary, dropping in relative humidity increases ET0 to some extent; (2) ET0 in spring was found to increase significantly (2966 mm per decade) , attributing to the decrease in relative humidity as well as the rise in maximum temperature, while ET0 decreased at a rate of -5451, -0922, -0207 mm per decade in summer, autumn, and winter, respectively; (3) the downward trend of ET0 in the three seasons was mainly related to the decline in sunshine durition and wind speed; (4) Annual wind speed, relative humidity and sunshine duration decreased while temperature, precipitation and wetness index showed an upward trend, suggesting a warming-wetting trend in Hunan Province; and (5) Spatial distribution of ET0 in Hunan Province under changing climate differed significantly among various regions both over annual and seasonal scale