Abstract: The experiment explores the impact of alkali stress on the growth and single root mechanical effects of herbs.Elymus nutans Griseb and Elymus sibiricus Linn are suitable to survive in cold and semi-arid environment in the Yellow River source region. They are selected as testing species. Through indoor cultivation, the two species are treated with different NaHCO₃ concentrations of 25mmol·L^-1, 50mmol·L^-1, 75mmol·L^-1 or 100mmol·L^-1.Meanwhile, NaHCO₃ concentration at 0mmol·L^-1 is taken as the control group. The plant height and relative survival rate of the two herbs are recorded. After being given alkali treatment, on the 15^th and 30^th day, their single root mechanical effect indexes and physiological indexes are determined respectively. Single root mechanical effect indexes include single root tensile resistance and single root tensile strength. The physiological indexes include proline content, malondialdehyde content, chlorophyll content, and relative conductivity. The test results are as follows:The impact of alkali stress on the single root mechanical effects of the herbs increases as concentration or growth time increases. When the concentration of alkali stress is 25mmol·L^-1,the single root tensile resistances of two herbs are greater than that of the herbs in the control group. When concentration of alkali stress is bigger than 25mmol·L^-1,the single root tensile resistances of two herbs are smaller than that in the control group. After being given alkali treatment, the single root tensile strength of the two herbs is greater than that in control group, with the amplification of 3%~16%.And with the same concentration, the single root tensile strength decreases 1%~18%with increase in growth time. In the case of the same growth time and concentration, the single root tensile resistance of Elymus sibiricus Linn is 0.13 N~0.53 N greater than that of Elymus nutans Griseb, and the single root tensile strength of Elymus sibiricus Linn is 20~65MPa greater than that of Elymus nutans Griseb. Based on gray correlation analysis, under the condition of alkali stress, among the determined four physiological indexes, chlorophyll content has the greatest correlation with the single root tensile resistance or the single root tensile strength of the two herbs. The correlation analysis 0.888~0.996 reflects that the single root tensile resistance and single root tensile strength of the two herbs are influenced obviously by relative conductivity. The study has theoretical value in further exploring the changing features and mechanism of root mechanical properties of herbs under the condition of alkali stress and in effectively preventing water and soil loss, shallow landslide and desertification which happen in salinized soil areas of the Yellow River source region.