In order to analyze the variation characteristics and influencing factors of reference crop evapotranspiration (ET_0) in Poyang Lake basin under the climate change, reference crop evapotranspiration (ET_0) from 1960 to 2014 was estimated with FAO-56 Penman-Monteith equation in 13 stations in Poyang lake watershed. The seasonally and annual changes of ET_0 and its causes were analyzed by using the Mann Kendall trend test, accumulative anomalies, sensitive curve and linear regression method. The results show that the annual average of ET_0 is 1 054.1 mm. Spatially, the ET_0 had an increased trend after an initial decrease from south to north, but the difference is not obvious. While seasonal difference is obvious, ET_0 in summer is 3.53 times as much as in winter. In recent 55 years, the ET_0 showed a declined trend except spring, which showed a significant downward trend in summer (P<0.01). The annual ET_0 population showed a significant downward trend (P<0.01), with an average annual rate of -1.09 mm·a~(-1), in which annual average temperature increase contribution to 0.55 mm, the relative humidity increase contribution to 0.47 mm, wind speed decreased contribution to -1.27 mm, the annual sunshine hours decreased contribution to -0.83 mm. Consequently, the change of ET_0 is primarily attributed to the significantly decreased sunshine duration and wind speed in Poyang lake watershed. Relative humidity is the most sensitive variable to ET_0 in general for study area, followed by air temperature, sunshine hours and wind speed. Research results for climate change impact on Poyang lake Watershed water resources assessment and promote the benign development of the ecological system have important scientific significance and application value.