Previous studies on response to salt stress in willows have focused mainly on the physiological response to single-salt stress; however, response to complex saline-alkali stress in willows has rarely been reported. The present study explored the physiological resistance characteristics of willow under complex saline-alkali stress, to provide a theoretical basis for willow cultivation in saline-alkali soils. The effects of complex saline-alkali stress on growth and osmotic adjustment substances were studied using willow (Salix psammophila ‘Yanliu NO. 1’) seedlings. The seedlings were treated with 12 types of saline-alkali stress with different salinity and alkalinity levels, simulated by two neutral salts (NaCl and Na₂SO₄) and two alkali salts (NaHCO₃ and Na₂CO₃) mixed in various proportions[A (NaCl:Na₂SO₄:NaHCO₃:Na₂CO₃=1:2:1:0), B (NaCl:Na₂SO₄:NaHCO₃:Na₂CO₃=1:9:9:1), and C (NaCl:Na₂SO₄:NaHCO₃:Na₂CO₃=1:1:1:1)] and concentrations (50, 100, 150, and 200 mmol/L). Under these conditions, plant height increment and malondialdehyde (MDA), free proline, and soluble sugar content in leaves were measured. The results showed that salt concentration was the main factor driving growth in Yanliu NO. 1. With increasing salt concentration and proportion of alkaline salts, plant height increment of Yanliu NO. 1 showed a decreasing trend, whereas the leaf MDA, proline, and soluble sugar content increased in different degrees. At 200 mmol/L, plant height increment under treatments A, B, and C was significantly lower (P < 0.05) than that under the control treatment (CK, 0 mmol/L), by 61.32%, 68.67%, and 73.02%, respectively. The leaf content of MDA, proline and soluble sugar in Yanliu NO. 1 did not differ significantly with increasing salt concentration under treatment A (pH 8.04). Under treatment B (pH 8.66), the leaf MDA content showed a significantly increasing trend at salinity > 100 mmol/L, whereas the leaf content of proline and soluble sugar increased considerably at salinity > 150 mmol/L. Under treatment C (pH 9.47), the leaf content of MDA, proline and soluble sugar showed a small variation at salinity of 100 mmol/L, whereas the leaves withered at salinity > 150 mmol/L. The results of this comprehensive analysis indicated that (1) the growth of S. psammophila ‘Yanliu NO. 1’ was subject to different degrees of inhibition under complex saline-alkali stress, (2) S. psammophila ‘Yanliu NO. 1’ could not tolerate stress at concentrations > 100 mmol/L of the three mixed saline-alkali solutions, and (3) the saline-alkali condition with salinity > 150 mmol/L and pH > 9.51 was not suitable for the growth of S. psammophila ‘Yanliu NO. 1’.