Abstract: The soluble salt ions contents of Populus alba L.var.pyramidalis growing in two kinds of salinity soil were studied.The results show that the soluble salt ion contents in the soil of waste canal are higher than those of irrigation canal，and there is significant difference between them except HCO₃^-and K⁺.But the differences in soluble salt ion contents are indistinctive in the parts of the trees above the ground growing at the same age in the two kinds of soil.There are obvious differences in the contents of Cl^-，Mg²⁺，Na⁺ and K⁺ in the roots of Populus alba L.var.pyramidalis.These demonstrate that the tree has certain repellent function to higher salt ions in the soil.Populus alba L.var.pyramidalis is able to control Cl^- and Na⁺ that bring poison to the tree in the roots and restricts them from getting into leaves，branch and trunk.The roots have strong selective absorbability to SO₄^2- and Ca²⁺ and can remove surplus SO₄^2- and Ca²⁺ out of the body.The roots of the tree have weak selective absorbability to Cl^-，Mg²⁺ and Na⁺.