Abstract: To understand the effects of precipitation increase and nitrogen addition on non-structural carbohydrates (NSC) of poplar seedlings, Populus × xiaozhuanica cv. Zhangwu seedlings were grown under a full factorial experimental design of two factors, i.e., three water treatments (W₁,natural precipitation; W₂, natural precipitation increased by 50%; W₃, increased by 100%) and four N fertilization levels (N₁,0 g N·m^-2·a^-1; N₂,5 g N·m^-2·a^-1; N₃,10 g N·m^-2·a^-1; N₄,15 g N·m^-2·a^-1). The results showed that changes in NSC contents in each organ of P. Zhangwu seedlings reflected significant interactions between precipitation increase and nitrogen addition. With the increase of precipitation, under the N₁ level, soluble sugar content was unchanged in leaves and branches, while the starch content decreased in leaves, branches, stems, coarse and fine roots. With the increase of precipitation, the soluble sugar content remained unchanged or declined, while the starch content decreased or firstly increased and then decreased in different organs under the N₂ and N₃ levels. The soluble sugar and starch contents increased or firstly decreased and then increased in different organs under the N₄ level. With the increase of N addition, the soluble sugar content remained unchanged and the starch content increased in leaves, soluble sugar content increased and starch content was unchanged in fine roots in the W₁ treatment. The soluble sugar content remained unchanged or firstly increased and then decreased, and the starch content decreased or firstly increased and then decreased in different organs in the W₂ treatment. The soluble sugar, starch and NSC contents increased in the W₃ treatment. In different precipitation and N addition treatments, the soluble sugar contents of P. Zhangwu seedlings ranged from 39.1 to 88.3 mg·g^-1, with the highest value observed in leaves and the lowest value in fine roots, and the starch content ranged from 23.3 to 46.8 mg·g^-1, with the highest in coarse roots and the lowest in fine roots.