Evapotranspiration (ET) plays a critical role in the cycles of matter and energy on the land surface. Understanding its spatiotemporal pattern and control factors is of great scientific importance. Intensive climate change in the past decades has been modifying the hydrological and heat fluxes profoundly. At the same time, the vegetation change will further complicates the dynamics of ET. Located at the middle reaches and southern bank of the Yangtze River, the Poyang Lake Basin experienced remarkable vegetation restoration and climate change during the past three decades, thus providing a valuable opportunity for us to evaluate the joint and respective effects from them. The main objective of the study is to estimate spatiotemporal patterns of ET in the Poyang Lake Basin and quantitatively evaluates the impacts from different environmental factors. We producted a long- term (1983-2011) ET record and investigated multidecadal changes in evapotranspiration and underlying causes in the Poyang Lake Basin with the application of WaSSI-C ecosystem model, which was driven by meteorological data, leaf area index data and basic soil parameter data. The modeled ET results were validated at different spatial scales and exhibited overall reasonable accuracies. According to the modeling results, substantial variations were detected in the spatial patterns of multi-year mean ET value across the Poyang Lake Basin (741-914 mm/a), which can be largely explained by the distributions of vegetation and precipitation. Over the past 29- year study period, ET record in the Poyang Lake Basin showed an upward global trend of 1.495 mm/a with large inter-annual fluctuatation. Based on the scenario design, our factor analysis further indicated that all changes of vegetation, precipitation and air temperature will lead to the positive ET reponses, while the joint effect of precipitation and air temperature will lead to a negative ET response. The overall upward trend of ET was largely derived from the contribution of vegetation restoration. Climate change, on the other hand, primarily explained its inter-annual variation.