Abstract: In this article,the achievement in the field of evapotranspiration research in the wand during last 200 years is reviewed.The main theories and methods for estimating evapotranspiration of crops or trees,including the hydrological,micrometeorological,plant physiological and rermte sensing methods,as well as dynamic simulating based on the water transport theories in soil plant atmosphere continuum (SPAC) are summarized.The application conditions,the performances and the problems in applications are discussed.The Hydrological methods can be used in many cases because of simplicity and unlimitedness by time and meteorological elements.The micrometeorological methods for calculating evapotranspiration,which not destray ground surface,can be used to measure an even formed stand.The plant physiological approach usually used to measure an individual tree.The remote sensing methods are under development.Although many problems remain to be solved,it is much useful for practice and looks very promising because it can provide regional evapotranspiration information.It is very accurate for measuring the evapotranspiration of plants and dynamic simulating based on water transport theories in SPAC.Based on those mentioned above,the future trends in evapotranspiration research of crops or trees are forecasted.