Abstract: The evapotranspiration，water use efficiency，radiation budget and energy balance of soybean field in the Sanjiang Plain are analyzed in this paper．The results show that the evapotranspiration capabilities of farmland are equal to precipitation during the crop growth Seaso n，the change of so ybean field evapotranspiration is sim ilar to the change of leaf area index．The ratios of net radiations to total radiation are different in different soybean growth stages and the value is 50％ in the sowing and seedling stage，increases to 60％ in the florescence and bear pods，finally decreases to 55％in the milking and harvesting time．The energy balance of soybean field has daily change and seasonal variation，the latent heat consumes 90％ of net radiation，the sensible heat and the soil heat flux are very small during the soybean growth Season．and the values respectively are below 1．5％and 10％．