Abstract: The actual evapotranspiration and water surfaca evaporation are observed by weighting lysimeter and E601 evaporation pan in the growing season of winter wheat in the North China Plain．The relative evapotranspiration of winter wheat(the ratio of the actual evapotranspiration to water surface evaporation)shows the characteristics of water depletion of winter wheat determined by soil water content and crop factors．Based on the analysis of the relationship between relative evapotranspiration and leaf area index and soil water content．an empirical function has been constructed ：RE =1n(1+ )(1．03+0,68 LAJ)．In the fie1d condhitions，the eva1uation of actual evapotmnspimtion by re1ative evapotranspiration and water surface evaporation provides a helpful information for irrigation scheduling of winter wheat．