Global hydrologic cycles have been intensified by climate change. However, the ways in which climate change affects the evaporation and surface energy budget over inland waters remain unclear. In this study, the surface energy fluxes were measured by an eddy covariance system over the Poyang Lake in August, 2013. We analyzed the hourly and daily variations of energy fluxes, and their responses to the environmental factors. The results showed that the latent heat flux (LE) has strong turbulence in diurnal variations compared with the sensible heat flux (H) over the Poyang Lake. Most of latent heat fluxes were positive values during the whole day, ranging in -50580 W/m~2. The sensible heat flux showed a weakly variance with a range of -50-50 W/m~2. The daily mean latent and sensible heat flux showed a decreasing trend with a large fluctuation in August, with the daily mean LE and H of 167.4 and 15.9 W/m~2, respectively. The sum of daily mean LE and H was larger than the net radiation in August, due to heat storage in water body release and supplement of LE and H. In hourly scale, the latent heat flux was out of phase with net radiation, and has a good relationship with the wind speed. In daily scale, the mean LE was mainly controlled by the wind speed and saturate vapor pressure deficit, and H was controlled by the wind speed and air temperature.