Abstract: Shrub and tree planting plays an important role in combating desertification in China′s Mu Us Sandland, an ecotone sensitive to both the environmental fluctuations and anthropogenic disturbances. Recent years has witnessed the success of establishing Pinus tabulaeformis tree-belt in purpose of wind-breaking and sand-fixing in this area. However, the growth of the Pinus trees is prevailingly constrained by shortage of water. This restriction can be furthered by the persistence of varied substrate conditions that lead to the differences in water availability to plant. As a result, it’s urgently needed to analyze the physiological performance of this plant growing at the specific soil substrates in this area. This paper studied the water relations ,including transpiration, leaf water potential and drought resistance ,of the Pinus trees growing at both the typical dune and hard ridge (Cretaceous and Jurassic rocks)substrates. The main results obtained are in the following. (1)In Spring time, the Pinus trees growing at the hard ridge experienced more serious drought than their dune counterparts. This implies that much care is needed for the hard ridge grown rtees in Spring time; (2)The density of the Pinus tree-belt at the dune site should be paid special attention to because soil water holding capacity was poorer at this substrate; (3)Osmotic potential at initial plasmolysis obtained from the Pressure-Volume curves can be regarded as the threshold points at which leaf tissue begin to be injured by drought stress, and hence can be an indicator for requirement of watering.