In order to analyze potential evapotranspiration in the past 55 years for trend of its variation and validate wheth⁃er and how"evaporation paradox"existed in Jiangxi Province, monthly meteorological data of the years of 1957-2011 were gathered from 15 national⁃level meteorological observatories in Jiangxi Province. On such a basis, potential evapotranspira⁃tion ( ET0 ) was calculated with the Penman⁃Monteith formula for analysis of spatio⁃temporal variation rule of ET0 with the spatial interpolation and data mining technology, partial derivatives of each variable of the Penman⁃Monteith formula de⁃rived, and causes of the ET0 variation and their sensitivities to each variable quantitated with the help of total differential and partial derivative coefficient of each variable. Results show that since 1970 annual mean ET0 in Jiangxi Province had been declining significantly, while temperature there rising remarkably, thus forming obvious “evaporation paradox”. Mean potential evaporation of a year, the flood season and the non⁃flood season was 0�20, 0�10 and 0�31 mm·d-1 , re⁃spectively, lower in the years after 1970 than in the years before that. Especially the decrease in sunshine hour and mean wind velocity caused the three indices to fall by 0�19 and 0�04, 0�25 and 0�04, 0�25 and 0�04 mm·d-1 , respectively. Meanwhile, the partial derivative of ET0 was the biggest to sunshine hour and mean wind velocity. Analysis in the study demonstrates that the rules of variation of ET0 and temperature in Jiangxi Province was mainly determined by duration of sunshine hour and mean wind velocity.%为分析过去55 a江西省潜在蒸发量的变化趋势，验证是否存在“蒸发悖论”及原因，根据江西省15个国家气象站1957—2011年的逐月气象资料，选取Penman⁃Monteith公式计算潜在蒸散量（ ET0），结合空间插值和数据挖掘技术分析ET0时空变化规律，对Penman⁃Monteith公式各自变量求偏导，以全微分和各自变量的偏导系数分别定量衡量ET0变化的成因和对各自变量的敏感性。结果表明，江西省年ET0自1970年起显著减少，气温显著上升，形成“蒸发悖论”，1970年后潜在蒸发量的年均值、汛期均值、非汛期均值相对之前分别减少0�20、0�10和0�31 mm·d－1，其中日照时数和平均风速减少分别引起年、汛期、非汛期ET0减少0�19和0�04、0�13和0�03、0�25和0�04 mm·d－1，且ET0对日照时数和平均风速的偏导数最大。分析认为江西省ET0和气温的差异性变化规律主要是由日照时数和平均风速引起的。
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