【Objective】 The aim of this study was to gain an understanding of the relationship between the chemical composition and mechanical properties of roots. 【Method】 We determined the tensile strength of roots, measured the contents of chemical components, including cellulose, hemicellulose and lignin; and assessed the surface appearance of the roots, with a view toward elucidating the protection mechanism of roots in the soil from a microscopic perspective. 【Result】 ① We found that root diameter had a considerable effect on tensile strength, namely, the larger the root diameter, the higher is the ultimate tensile force, and the smaller are the ultimate tensile strength and ultimate elongation. ② The effects of root diameter on chemical composition were consistent with those of mechanical properties, with the contents of cellulose and hemicellulose increasing, whereas that of lignin showed a decrease. Furthermore, we found that whereas the lignin content ofPyracantha fortuneana was higher than that of Rhamnus dumetorum Schneid, the cellulose content showed the opposite pattern. ③ In terms of toughness and strength, the microscopic chemical structures of cellulose, hemicellulose and lignin had a marked influence on the macroscopic mechanical properties of roots, with a higher lignin content being associated with a greater ultimate tensile strength and tensile resistance, and higher contents of cellulose and hemicellulose being associated with a smaller ultimate elongation. ④ The surface of roots at the microscopic level was observed to be a “porous structure,” similar to that of the wood, and accordingly is assumed to confer the root system with mechanical strength.【Conclusion】 Collectively, our results revealed that inherent factors that influence the mechanical properties of the root to a certain degree provide a theoretical basis for the selection and optimization of tree species for ecological restoration of slope landscapes.