Abstract:Based on the data of the whole year in 2005, including the microclimate gradient observation data, eddy covariance observation data, and ecophysiological observation data in Panjin Wetland Ecosystem Research Station, Institute of Atmospheric Environment, China Meteorological Administration, the daily evapotranspiration variation and its controlling factors of Phragmites communis community was analyzed. The results showed that the daily evapotranspiration variation in different months could be expresses as a single peak curve that was lower in the morning and evening and higher around noon. meteorological factors and biological factors would affect the evapotranspiration. According to the correlative analysis, the evapotranspiration variation of Phragmites communis wetland has good responding to the environmental factor such as radiation, air temperature, surface temperature, relative humidity, wind speed and soil moisture. Regression analysis indicates, the major factors ingrowing season are: radiation, soil moisture, relative humidity, air temperature and surface temperature; the factors in non-growing season are: radiation, surface temperature and wind speed. At the same time, vegetation growth situation and biological characteristic had significant effects on the evapotranspiration of Phragmites communis, especially, leaf area index, leaf transpiration rate and leaf conductance.