[Objective] The biological diversity and the anti-tensile mechanical properties of plant roots in the Ngoring Lake area were investigated, to provide data support for the effective prevention and control of geological disasters such as soil erosion and the sod layer slump of alpine grassland in the Ngoring Lake area, the source of the Yellow River, as well as a theoretical basis for the research on the failure mechanism of the sod layer. [Methods] Based on the sample survey results in the study area, single-root tensile tests were performed on the dominant herbaceous plants in the area; the differences in single-root tensile strength, single-root tensile intensity, single-root ultimate elongation and single-root modulus of elasticity of the different herbaceous plants and their relationship with the root diameter were comparatively analyzed in different root-diameter levels. [Results] The dominant herbaceous plants in the study area were Carex moorcroftii, Astragalus polycladus, Artemisia frigida, Poa annua, Leontopodium pusillum. and Lagotis brachystachya. Under the condition of root diameter range of 0.10—0.60 mm, the single root tensile strength and single root tensile intensity of the above six herbaceous plants exhibited the trend of power function growth and power function decrease, respectively, with the increase of root diameter. Furthermore, there was no significant functional relationship between the single-root ultimate elongation and single-root elastic modulus and root diameter. Considering the mechanical property indexes of single root tensile resistance, species importance value, and root type of different plant types, Poa annua exhibited the best soil fixation capacity in the Ngoring Lake area. [Conclusion] The root systems of the six dominant herbaceous plants in the study area have better soil-fixing potential, among which Poa annua has the strongest soil-fixing ability. This study’s results can provide a certain basis for the soil and water conservation work in the Ngoring Lake area.