Abstract: The mathematical expression of the strength of the reinforced soil is theoretically deduced, and the influence of the soil cohesion and the soil-reinforcement interface parameters on the strength of reinforced soil is analyzed. It is shown that when the reinforced soil is subjected to the tensile load up to failure, the cohesive force is reduced to an extent as compared with the tensile force provided by the reinforcement, the strength of the reinforced soil will be less than that of the plain soil; when the reinforced soil is adhesively damaged, the strength of the reinforced soil is less than that of the plain soil when the cohesion are reduced to an extent as compared with the friction provided by the reinforcement. The degree of reduction of the strength of the reinforced soil is related closely to the degree of the interlayer formed by the reinforced material in the soil, the permeability of the soil-reinforcement interface, the spacing of the reinforcement and the indirect reinforcement range.