Assuming that the failure surface to be an inclined plane through the slope toe

and based on the classical plasticity theory and the generalized plasticity theory respectively

the computation formulas of the reinforced slope’s critical height are deduced. Comparing to the previous experimental values of the reinforced slopes

although the critical height with the generalized plasticity theory limit analysis method is slightly higher than the critical height with the classical plasticity theory limit analysis method

and it is more close to the experimental values; both of them are reliable in the engineering; and they can be used as reference for reinforced slope design .