The comparative study of physiological reaction to salt, alkali and mixed salt stresses in two ecotypes of grey-green and yellow-green of Leymus chinensis were made. At the stage of seedling, the content of chlorophyll and the leakage rate of electrolyte of leaves, free proline, Na/K of tillers were determined in planting containers with sands in two ecotypes by stress of salt, alkali and mixed salt of different concentrations. The results of quantitative analysis showed that the relationships between the content of chlorophyll and the leakage rate of electrolyte of leaves, free proline, Na/K of tillers and concentration of salt, alkali and mixed salt could expressed as linear equation, which were significant or obviously significant. There were capabilities of salt-alkali resistance in the physiological characteristics of two populations, but the capabilities of salt-alkali resistance were stronger in grey-green ecotype than in yellow-green ecotype. The differentiation of the content of chlorophyll, the leakage rate of electrolyte of leaves, free proline and Na/K of tillers were significant or obviously significant in two ecotypes under three kinds of salt stress. Physiological characteristics of salt-alkali resistance were significantly different in two ecotypes. The study provided physiological evidence for making sure that the main ecological factor was salt-alkali. It resulted in adaptive differentiation in Leymus chinensis ecotypes.