[Objective] The effects of single root pulling strength on the shear strength of slope soil were investigated, and the effect of root on the shear strength of slope soil was quantitatively analyzed in order to provide a basis for evaluating the shear strength of slope soil strengthened by plant roots.[Methods] The root-soil complex of 2-year-old Hypericum acmosepalum was studied. The indoor single-strand pull test and the root-soil composite shear test were conducted to obtain the tensile strength of the root system. The relationship between the root tensile strength and the cohesion force of the root-soil composite was analyzed.[Results] There was a negative power function relationship between the tensile strength and root diameter of H. acmosepalum, and the correlation coefficient was greater than 0.92. The root pullout displacement and tensile force were positively correlated with root diameter, and there was also a significant positive correlation between the pullout displacement and tensile force. The tensile strength was negatively correlated with root diameter, the pullout displacement and the pullout force, and the cohesive force of the root-soil composite increased by 17.25%~94.76%, compared with that of the rootless soil. The cohesion and cohesion growth rates were positively correlated with root-soil area ratio and root-soil volume ratio.[Conclusion] The pullout characteristics of the H. acmosepalum root have a significant influence on the shear strength of the slope soil, and the evaluation indexes of the shear resistance of the slope soil are closely related to the changes of the root pullout characteristics.