Aiming to solve the contradiction between demand for the extension of forest vegetation and the limited water supply in arid and semi-arid area, the dissertation chose the main afforestation tree species and typical vegetation communities in Gu Yuan City in the north of LiuPanshan mountains, utilized advanced apparatus, equipments and various approaches, at leaf, tree and community scales, systematically studied the ecophysiological characteristics of plant transpiration and water consumption, rules governing water consumption of tree and community and their control mechanism by environmental factors. These studies could provides scientific bases for accurately estimating ecological water consumption and the choice of drought-tolerance and water-saving afforestation tree and herb species, as well as the properly arrangement of stand density. The dissertation involved following aspects:* The study on ecophysiological characteristics of 13 main afforestation tree and herb species* Transpiration and water consumption of the 3 typical vegetation communities, at whole-tree and stand scale, and under two levels of stand density.* Total and component proportion of evapotranspiration of the three typical vegetation communities at two stand density levels.* Simulation and prediction of stand transpiration and water consumption of 13-year-old Larix principi-rupprechtii Major conclusions are summarized as follows: 1) Under the condition of free soil water stress, the transpiration rate of coniferous trees was the lowest, whilst the broad leaved trees were the highest, and the shrub species fell between coniferous species and broad leaved species.When sorted by potential transpiration rate and stomatal conductance, the increasing orders were: Picea wilsonii Mast.、Platycladus orientalis、Pinus tabulaeformis、Caragana korshinskii、Fraxinus americana L.、Prunus armenniaca var. ansu Maxim、Ailanthus altissima、Hippophae rhamnoides、Ulmus pumila L. and Robinia pseudoacacie L..2) Positive correlation was found between the transpiration rate of seedling and predawn leaf water potential, that is, with the decrease of leaf water potential, transpiration rate reduced exponentially. According to the potential transpiration rate and its sensitivity toleaf water potential, the ten tree seedlings could be divided into four groups as follows: Picea wilsonii Mast.、Platycladus orientalis、Caragana korshinskii and Fraxinus americana L., with low-transpiration-rate-and-insensitive-to-water-stress; Pinus tabulaeformis, belonging to low-transpiration-rate-and-sensitive-to-water-stress species; Ulmus pumila L.、Robinia pseudoacacie L.and Hippophae rhamnoides are of high-transpiration and-sensitive-to-water-stress species, and Prunus armenniaca var. ansu Maxim and Ailanthus altissima are of medium-transpiration-rate-and-sensitive-water-stress species.3) The results of ecophysiological measurements under different soil water status indicated that Larix principi-rupprechtii is a low-transpiration-rate-and-sensitive-to-water-stress specie, and its' transpiration was mainly controlled by stomatal. As a result, Larix principi-rupprechtii can be selected as a drought-tolerance and low water consumption specie in afforestation in arid and semi-arid areas. Prunus davidiana is a high-transpiration-rate-and-insensitive-to-water-stress species that could be planted in sunny slope where soil water content is low. Medicago sativa is a high-transpiration-rate-and-sensitive-to-water-stress species thus should be careful to use the species for artificial grassland establishment.4）Diurnal course of sap flow of Pinus tabulaeformis and Larix principi-rupprechtii changed regularly from night to day, usually it was very weak in nighttime and started to increase continuously to single-peak or multiple-peaks in the daytime. Relatively, the maximum of sap flow of Larix principi-rupprechtii was lower but the period that kept on the peak was longer , on the contrary, the maximum of sap flow of Pinus tabulaeformis was high