[Objective] This paper aimed to explore the drought resistance mechanism of Populus simonii, and to provide a scientific basis for the construction of the shelterbelt in the northern of Shanxi Province.[Methods] The effect of drought stress on Populus simonii seedling growth was studied based on the pot experiment conducted in the Taidu nursery base of Jixian Forestry Bureau in the southwest of Shanxi Province. The experiment simulated drought conditions and used the Populus simonii from a loess gully region as the provenance material. And height and ground diameter of the seedling, the biomass in leaves, stems and roots, the relative water content and water potential, net photosynthetic rate, transpiration rate and other growth and physiological indexes were measured in order to study the effects.[Results] The results showed that drought stress inhibited the growth of the Populus simonii seedlings, including the aboveground parts and the root system; Leaf relative water content and water potential decreased with the reduction of the relative water content of soil. In different drought gradient treatments(CK,T₁,T₂,T₃,T₄,T₅), net photosynthetic rate and transpiration rate slowed down with the severeness of drought stress. However, in the treatments of CK(field capacity) to T₃ (40% of field capacity, soil water content is 8.12%), the declined rates were gradually smaller; in addition, the Populus simonii seedlings could maintain a relative large photosynthetic rate and transpiration rate, which indicated that Populus simonii had obvious drought resistance. When soil moisture further reduced, Populus simonii appeared to be drying in the period of T₄ (30% of field capacity, soil water content is 6.09%), and in T₅ (20% of feild capacity, soil water content is 4.06%) all died.[Conclusion] In the southwest of Shanxi Province and the surrounding areas, soil water should be stayed above 6.09%(T₄) as far as possible while planting Populus simonii.