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Potential evapotranspiration(ETo) is important to hydrological cycling and the global energy balance.Based on a modified FAO56-Penman-Monteith model,ETo was simulated for 603 meteorological stations across China in the period 1971-2008.Spatial distribution and temporal change of ETo were characterized,and the determining factors in ETo were revealed by sensitivity analysis.Results show obvious regional differences in annual average ETo and its determining factor.In general,annual average ETo decreased in the period 1971-2008,but increased since the 1990s.Wind speed and sunshine duration were determining factors in the annual ETo trend,with smaller contributions from relative humidity and temperature.Declining wind speed was the determining factor in decreasing annual ETo in northern temperate regions and the Tibetan Plateau.The spatial extent of wind speed influence contracted to northwest China in summer,and expanded to the whole country in autumn.Decreasing sunshine duration was the determining factor in decreasing annual ETo in subtropical and tropical regions,especially in summer,with a larger spatial influence mainly to the southeast of the farming-pastoral region.ETo change has distinct impacts on earth surface ecosystems and environment depending on different determining factors.