Abstract: Abstract: To further explore the mechanical effects of roots of herb species on soil reinforcement and slope protection in loess region of Xining Basin, in this study, 3 kinds of herbs i.e. Elymus nutans Griseb., Agropyron trachycaulum Linn. Gaertn. and Medicago sativa L., which were planted in the self-established testing area in Xining Basin, were selected as the research objects and the growth time was 150 d. Under the condition of different root diameter levels, single root tensile force, single root tensile strength and single root limit extensile rate of 3 kinds of herbs were assessed via single root tensile test. Furthermore, the stress-strain characteristics of 3 kinds of herbs during the tensile process were further analyzed. The test results are as follows: Under the 5 levels of root diameters i.e. (0.10, 0.20, (0.20, 0.30, (0.30, 0.40, (0.40, 0.50 and (0.50, 0.60 mm, the single root tensile force of M. sativa, E. nutans and A. trachycaulum ranges from (2.28±0.67) to (12.00±3.89) N, from (1.75±0.43) to (7.66±0.72) N and from (1.82±0.46) to (7.95±0.47) N, respectively; the single root tensile force of M. sativa is averagely 1.32 times higher than E. nutans and 1.26 times higher than A. trachycaulum; the single root tensile strength of M. sativa, E. nutans and A. trachycaulum is from (49.21±17.06) to (124.88±46.63) MPa, from (35.33±1.76) to (84.87±15.93) MPa and from (35.96±2.46) to (73.32±19.56) MPa, respectively; the single root tensile strength of M. sativa is averagely 1.30 times higher than E. nutans and 1.31 times higher than A. trachycaulum; the single root limit extensile rate of E. nutans ranges from 50.36%±15.52% to 76.4%±3.05%, which is averagely 1.13 times higher than A. trachycaulum (from 45.84%±11.56% to 73.28%±10.82%) and 2.16 times higher than M. sativa (from 25.74%±8.05% to 36.09%±7.78%); in addition, when the root diameter is from 0.10 to 0.60 mm, the single root tensile force of the 3 kinds of herbs increases with the root diameter increasing, with a power relationship between single root tensile force and root diameter. Meanwhile, the single root tensile strength of the 3 kinds of herbs increases with the root diameter decreasing, and a power relationship exists between single root tensile strength and root diameter; moreover, the single root limit extensile rate of the 3 kinds of herbs increases with the increasing of the root diameter, but there is no significant functional relationship between them. The 3 kinds of herbs show 2 types of stress-strain curves (Ⅰand Ⅱ) during the single root tensile test; both of 2 types of stress-strain curves for the 3 kinds of herbs can be divided into 4 stages: elastic deformation, elastic-plastic deformation, strain hardening and fracture failure; in addition, the stress-strain curves of Type Ⅱ have the phenomenon of double peaks, which is due to the epidermis of root broken earlier than its internal tissue; the stress-strain curves of Type Ⅱ are found in the single root tensile process of E. nutans and A. trachycaulum, but not in M. sativa, which means the stress-strain process of root epidermis and its internal tissue of M. sativa has a relatively significant synchronism during the single root tensile test; it can also be concluded that, among the 3 kinds of herbs, M. sativa has the most significant effect on enhancing soil shear strength, followed by A. trachycaulum and E. nutans. These conclusions have a theoretical and practical significance in preventing soil erosion, shallow landslide and other geological hazards in cold and arid environment.