The uptake, transport and distribution of K+, Na+ and Cl- in different parts of Populus Euphratica and Populus bolleana Lauche seedlings under different NaCl stress conditions were investigated to study the salt tolerance mechanisms of the two poplar species. The results showed that: (1) The concentration of K+ declined, Na+ and Cl- increased in the two poplars under NaCl stress. The concentration of K+ showed the highest level in leaves, the less in stem and the lowest in root. The order of Na+ concentration was as follow: leaves > root > stem. The Cl- showed different distribution patterns between P. euphratica and P. bolleana, and the leaves contained more Cl- ion than in root for P. euphratica, however, the root contained more Cl- than in leaves for P. bolleana. The Cl- concentration was the lowest in the stem for the two poplar species. NaCl stress showed less effect in K+ and Na+ level in P. euphratica than in P. bolleana, and Cl- concentration increased less in P. euphratica root and stem than those of P. bolleana under NaCl stress. Compared with P. bolleana leaves, there was more significant Cl- level rise in P. euphratica leaves. (2) The K+/Na+ ratios in the two plants declined with the increasing of NaCl concentration. The K+/Na+ ratio was significantly higher in all organs of P. euphratica than that of P. bolleana except for stem exposed under low NaCl concentration. Compared with P. bolleana, P. euphratica had a lower transport selectivity of K+ to Na+ from root to stem, but had a higher transport selectivity of K+ to Na+ from stem to leaves, and retained more Na+ in roots. (3)With the increase of NaCl concentration, the transport selectivity of Cl- to Na+ from root to stem decresed in P. euphratica, but it decreased firstly and then increased in P. bolleana. Compared with P. bolleana, the transport selectivity of Cl- to Na+ from root to stem in P. euphratica was significantly higher, but the transport selectivity of Cl- to Na+ from stem to leaves was lower (except for 2% NaCl treatment). The results indicated that P. euphratica accumulated saline ions mainly in roots to resist salinity stress, while P. bolleana accumulated saline in stems. The salinity-resistant of P. euphratica was better than that of P. bolleana because the P. euphratica had better cell salinity-resistance, better compartmentalization of saline ions in cell vacuoles, and better maintenance of the K+/Na+ balance.