Abstract: Daily changes of transpiration rate of six tree species for city greening in Beijing and water consumption status in different densities were studied by using Lico-6400 and BP3400 and press chamber etc. Then day and night variation and the daily variation of water consumption potential of the six tree species and the factual water consumption rate were compared. The results show that the rules take on "single peak style" in normal water supply, and the peak value appears between ten o'clock and fourteen. When the density is one, these six species have the average transpiring water consumption amount in the following order:Sophora japonica>Fraxinus velutina>Platycladus orientalis>Pinus tabulaeformis>Syringa oblata>Buxus sinica. The average transpiring water consumption rateis in the following order:Fraxinus velutina>Sophora japonica>Syringa oblata>Buxus sinica>Platycladus orientalis>Pinus tabulaeformis. And the transpiring water consumption rates of broad-leaf tree species are much greater than coniferous species. With the increase of the density, water consumption amount increases quickly but the water consumption rate decreases. With the increase of the density, the average transpiring water consumption rate of the six species is in the following descending order:Pinus tabulaeformis is the largest, while Sophora japonica is the smallest, and Fraxinus velutina, Platycladus orientalis, Syringa oblata, Buxus sinica are in the middle.