Abstract：The single root tensile and shear tests were carried out to study the mechanism of slope protection by shrub roots and analyze the mechanical characteristics of shrub roots on Caragana korshinskii，Nitraria tangutorum，Zygophyllum xanthoxylon and atriplex canescens in loess area of Tibetan plateau where Xining basin was taken as an example. Experiments and studies showed that power or exponential relations existed between single root tensile resistance and root diameter of four shrub roots，and both the single root tensile resistance and shear resistance increased with increasing diameter，and the increment rate of Atriplex canescens is the largest，followed by Caragana korshinskii、Zygophyllum xanthoxylon and Nitraria tangutorum for eighteen-month age shrub. Either power or exponential relations were fitted between root tensile strength and root diameter，and the root tensile strength decreased with increasing diameter. The results revealed that various root structures have different tensile stress-strain characteristics. The stress-strain curves of four shrub roots also presented straight line relation in root initial stage after tension. As the pulling force kept increasing after loading over elastic limit，the stress-strain curves reflected the non-linear elastic characteristics. The rate of tensile elongation of four shrub roots was all over 13%，and the elongation rate of roots decreased with increasing diameter. The shallow soil of studied area from 0.3 m to 0.8 m with plenty of hair roots had strong single root tensile strength，shear strength and non-deformability，so the shallow soil played an important role in controlling soil and water loss of slope，reinforcing shear strength of soil-root composite and controlling slide deformation. According to the root mechanical characteristics and root morphological features，Atriplex canescens and Caragana korshinskii had significant function in slope protection in of loess area Tibetan.
