Soil salinization has produced severe consequences on global agricultural production and ecological environment. Based on the features of saline soils in China, through mixed NaCl, NaHCO₃, Na₂SO₄, and Na₂CO₃ at varying ratios to simulate the salinity–alkalinity stress and conducted a controlled pot experiment using De Wit replacement method. The effects of salinity–alkalinity stress on the growth of Aegilops tauschii and its competition with wheat were explored to provide a reference for the study of invasion mechanism of A. tauschii. The result showed that, the salinity–alkalinity stress inhibited the growth and development of both the species, which was reflected in plant height, leaf area and total biomass indicators. Secondly, the tolerance of both plant species to salinity–alkalinity stress was improved by increasing the superoxide dismutase (SOD) activity and the proline content. However, as the salinity–alkalinity stress was exacerbated, the relative conductivity and thiobarbituric acid (TBARS) content increased significantly in both the species. As suggested by the level of increase in SOD activity, proline content, relative conductivity, and TBARS content, A. tauschii was more tolerant to the salinity–alkalinity stress than wheat. Finally, it can be seen from the value of the competition balance index, A. tauschii was still more competitive than wheat even under salinity–alkalinity stress. In summary, A. tauschii was more tolerant of the salinity–alkalinity stress than wheat through the favorable adjustment of morphology, biomass allocation pattern, and physiological features, which is expected to increase its invasion damage to wheat.