Abstract: By means of theoretical analysis and test investigation, a strength model of reinforced soil is pre-sented, which includes: (1)Judgement criterion for types of failure of reinforced soil, the critical confining stress σ30 of slippage and rupture failure is given. (2) Equation of limiting equilibrium conditions for two types of failure. (3) Failure envelope of reinforced soil. Conclusions were drawn that the slip failure envelope is a straight line, passing origin with inclination angle φR>φ, and the rupture failure envelope is a straight line with inclination angle 0 and pseudo cohesion CR. Equations of fa and c* are give. Comparison with test results shows this model can be used to predict the type of failure, failure envelope; and major principal stress at failure accurately. The stress-strain behavior of reinforced soil is analyzed. Conclusions are of great significance to internal stability analysis of reinforced soil structures.