Abstract: In this paper, daily reference evapotranspiration (ET₀) was computed with the recommended FAO-56 PenmanMonteith equation for Anhui Province using data collected 60 weather stations during 1961 to 2010 and its temporalspatial variations were characterized. The determining factors in ET₀ trends were inquired into through partial derivative quantification analysis for the study region. Results showed that the mean annual ET₀ was 878.58 mm·a^-1 over the whole region during the study period. ET₀ was the highest in summer and the lowest in winter. The mean annual ET₀ decreased from the north to the south and from low altitude regions to high altitude regions. Both sunshine duration and wind speed were the dominant factors contributing to the interannual change of ET₀, with less contribution from air temperature or relative humidity. The annual ET₀ showed a general decline at a rate of -1.61 mm·a^-1 owing to a more negative contribution of sunshine duration and wind speed than a positive contribution of air temperature and relative humidity. ET₀ increased insignificantly in spring and decreased slightly in both autumn and winter. However, it decreased significantly at a rate of -1.37 mm·a^-1 in summer. The main impacting factor was wind speed in spring, autumn and winter, but it was sunshine duration in summer. Great differences in the determining factors of the mean annual ET₀ existed from area to area in Anhui Province. The wind speed was the determining factor for 36.7% of the whole stations distributing in the southern part of the area north to the Huaihe River and the area along the Huaihe River, while the sunshine duration was the determining factor for the other regions.