Abstract: This paper mainly analyzed the transpiration characteristics of some trees for forestation in the Loess Plateau.34 kinds of arbors,brushes and fruit trees were determined as trial species,by means of artificial control watering soil water content gradually declined from field capacity to wilting point,while transpiration rates,stomtal sizes,leaf potential,saturated deficit,gross radiation,air relative humidity,air temperature,soil water content and leave area and so on were observed,moreover the relation of transpiration rates of various seedlings to these factors was analyzed.The results show that Chinese arborvitae(Piatycladus orientalis) responds the most sensitive for water stress and can quickly adjust its stomtal open degree to increase stomatal resistance to decrease transpiration rate.This is important physiology foundation that it has ability of strong drought resistance.The apricot(Prunus sibirica) and elm(Ulmus pumila) have higher critical saturated deficit and lower relative water content,therefore have stronger ability of bearing drought.That leave water potential of some trees with a sensitive reaction to transpiration rate can be used as the main factor that predicts transpiration rate.At more than 6% soil water content,the soil water content has a close relation with the transpiration rates of the seedlings,but does not has closely the relation at less than 6% soil water content.Transpiration rates of different tree species react to different environmental factors including atmosphere temperature,atmosphere humidity and gross radiation,so we can choose the factors of close relation with the transpiration rates of different seedlings so as to predict their transpiration rates.It is very important to increase the survival rate of forestation through site selection and rational utilization of soil moisture as to catch hold of chance of forestation at arid and semiarid regions on the basis of the relation ship between the transpiration rates of the seedlings and environmental factors like soil water content.