According to the ecological damage and instability of highway slopes, a theoretical research on the mechanism of ecological protection slope and an experimental study of the tensile of roots for its anchoring ability were presented. It has been proved in theory that soil shear stress is transferred to roots tensile stress through the frictional force of root-soil contact surface to improve soil shear strength, and soil granules around roots surface are aggregated through much high polymer produced from the growth of roots to resist slope soil erosion by rain. The tests have been based on the tensile strength of the roots of young robinia pseudoacacia. The results have shown that the maximum tensile strength of lateral root is higher than the maximum tensile strength of taproot, and the maximum value is up to 91.41MPa. Compared with the design tensile strength 210MPa of steel HPB235, its tensile strength is as great as 1/4~1/2.