Abstract: The characteristics of water capacity of branches and stems of Pinus tabulaeformis were studied in this paper to further illustrate the laws and controlling mechanisms in water consumption of forest tree species, and then provide a theoretical guidance for water management and the afforestation of P.tabulaeformis.Results showed that the diurnal fluctuation of branch relative water capacity of P.tabulaeformis decreased first and rised then.The branch water capacity and water potential assumed inverse function relations.The seasonal variations of relative water capacity of branches were influenced by the factors of soil and environment.And the size of water capacity was larger in June than that in September.Spatial variations of the relative water capacity of branches at different parts and directions had some differences, ie the upper crown's must be slightly larger than that of the below, and the southeastern must be slightly larger than that of the northeastern.Sap flow flux was influenced by sapwood area size, and decreased progressively from the base along the trunk to the top of tree.Deficit of water capacity of the top stem sections may receive supplement at night.As to its impact on the transpiring water consumption, the top tree body's storing water is dissipated first, then draws the lower position in turn, until the root system absorbs water actively.