In order to explore the mechanical property of Quercus mongolica roots, the drawing machine fixture was improved and the roots were preprocessed before the test, and Quercus mongolica roots of which diameter between 1 and 17 mm were picked out to conduct single root tensile test indoor under different gauge length. The results show that tensile resistance of Quercus mongolica roots increase with the increase of root diameter according to a power function, and its tensile strength decreased with the increase of root diameter. Moreover, the stress-strain curve of single Quercus mongolica root was a single-peak curve under different diameter class which exhibiting the elastic-plastic material characteristics. It indicates that the Quercus mongolica root has positive effects on maintaining slope stability through strong ability of tensile properties and deformation ability.