In order to research the mechanical characteristics of artificial slope protection by woody plants, the single root tensile tests were conducted indoors to study these properties of Ulmus pumila, Amorpha fruticosa, Robinia pseudoacacia and Lespedeza bicolor with 395 samples in Jing-cheng (Ⅲ) expressway where man-made slope was taken as an example. The contents of cell wall components of woody plants were determined such as hemi-cellulose, cellulose, lignin and holo-cellulose after classified into five root diameter classes, and then their mechanical properties were investigated by a systematic analysis. The results showed that a significant difference in tensile force and tensile strength existed between the four woody plants, in descending order as Ulmus pumila, Amorpha fruticosa, Robinia pseudoacacia and Lespedeza bicolor. The root tensile force varied from 22.18 to 464.50 N and tensile strength was in the range of 7.66-36.94 MPa with diameters of 0.95-5.42 mm. The root tensile force increased in power function with the increasing root diameter, meanwhile, the root tensile strength decreased in power function and inverse function with the increasing root diameter. The cellulose contents varied from 20.57% to 36.91%, the lignin contents from 15.12% to 29.84%, the hemi-cellulose contents from 1.37% to 29.26%, the holo-cellulose contents from 28.18% to 66.17%, and the content ratio of lignin to cellulose from 0.45 to 1.31. The cell wall components showed significant differences between different species and different diameters of root. The root tensile force was negatively correlated with lignin; the root tensile strength was positively correlated with lignin, but negatively correlated with hemi-cellulose. The results revealed that various root structures have different tensile stress-strain curves. The stress-strain characteristics of the single root presented straight line relation in the initial phase after tension. When the tensile force kept increasing after loading over elastic restrict, the stress-strain curves presented plastic characteristics gradually. According to the root cell wall components and root tensile properties,Ulmus pumila and Amorpha fruticosa had better performance in slope protection in the Jing-cheng expressway (Ⅲ).