Abstract:The authors summarized the main theories and methods in the research of forest evapotranspiration,which are lysimeter,ventilated chamber,eddy correlation,water balance,energy balance,EBBR,Penman-Monteith,SPAC,experience formula and remote sensing methods,and the problems in applications were discussed.The use of scintillometer to measure sensible heat flux and the use of double frequency macrowave radiometer to gain the capacity of atmospheric water vapor and cloud liquid water were introduced.Finally,the idea to acquire the quantity of evapotranspiration by the analysis of atmospheric water vapor balance was proposed,and the future trends in forest evapotranspiration research were forecasted.