[Objective] The tensile strength tests were carried out of the main roots and lateral roots of four shrub species in the loess area of Northeast Qinghai-Tibet Plateau, and the relationship between mechanical properties of main roots and lateral roots was discussed, which provided a reference for investigating the mechanical mechanism of plant roots in stabilizing soils and slopes.[Methods] The drainage area of Changlinggou in Xining Basin was selected as the studying area, and the tensile force, tensile strength, Young's modulus were measured by laboratory single root tensile test of four three-year-old shrub species(Caragana korshinskii, Lycium chinense, Nitraria tangutorum and Sarcozygium xanthoxylon).Then the relationship between root diameter, tensile force, tensile strength and Young's modulus of main roots and lateral roots of four species was further analyzed.[Results] The tensile forces of main roots of C. korshinskii, L. chinense, N. tangutorum and S. xanthoxylon were 28.45, 13.21, 11.01 and 7.35 times of lateral roots, the tensile strengths of main roots were 0.67, 1.17, 0.68 and 1.22 times of lateral roots, and the Young's moduluses of main roots were 2.00, 2.39, 2.82 and 2.48 times of lateral roots, respectively.[Conclusion] The tensile forces of main roots were significantly higher than lateral roots for four shrub species. The tensile strengths of main roots of C. korshinskii and N. tangutorum were lower than lateral roots, while the tensile strengths of main roots of L. chinense and S. xanthoxylon were higher than lateral roots. The Young's moduluses of main roots were significantly higher than lateral roots for four species, it showed that the main roots were not easy to deform in comparison with the lateral roots, and the contribution of main roots to the stability of the shallow slope is significantly higher than lateral roots.