Abstract: Since 1955 Mongolian pines have been introduced and planted on the sand land of Zhanggutai District. They shows stable performance and quick growth in general. Water content in the plant-root-layer of soil tends to descrease. In arid years, the growth and development of the trees are seriously affected. If the precipitation decreases by 10 mm., the tree height reduces around 0.5—15cm and the D.B.H. reduces 0.034 cm. Drought causes the needle to fall early than usual and also decreases the intensity of transpirat'on and photosynthesis of the trees, but, promotes fruit setting.