[Objective] The calculation method with regard to the carrying soil stability in a vegetation restoration project performed on the rock slope was discussed.[Methods] The acting forces both from resisting shear root and friction root were simulated, and then converted them into anti-shear strength and served as an added value to the stability of carrying soil. Further, a mathematical model associated with the soil stability on the rock slope was established, and was verified by the vegetation restoration project of the Jinan-Laiwu expressway.[Results] (1) The stability coefficient of carrying soil was a function of shear strength without root(F_s), bulk density(γ), thickness(d), and increment of root shear strength(τ_R). (2) The anti-shear strength of the root could be the sum of resisting shear root(τ_Rg) and friction root(τ_Rg). (3) The stability coefficient is persistently smaller than its measured counterpart, and the deviation rate is small. Also, the soil stability coefficient was positively correlated with the initial vegetation restoring period (i.e. 3~5 years).[Conclusion] The determination of carrying soil stability coefficient could be employed as the parametric design and evaluation for the vegetation restoration project on the rock slope.