Abstract: During the period from May to October 2006,the continuous eddy covariance measurements is used to investigate the seasonal variation of energy balance and evapotranspiration and to determine the total evapotranspiration over the typical marsh wetland in Sanjiang plain.According to the regression analysis,the total evaporation and transpiration are estimated.The results show that there is obvious seasonal variation of the energy balance of marsh wetland.Overall,the latent heat flux dissipated 45.5% of the net radiant energy,sensible heat flux 27.9% and the storage heat flux 26.7%.The total evapotranspiration from May to October is 310.6 mm,and the highest month-average daily evapotranspiration appears in July.The total evaporation which accounts for about 71% of total evapotranspiration is about 221 mm,and the total transpiration accounts for 29%.Therefore,the evaporation is the main contributor to the evapotranspiration over marsh.