Based on the tri-axial tests, the stress-strain relationship and strength properties of reinforced expensive soils are studied to get the relation between the strength index of reinforced soil and that of the corresponding plain soil. According to stress-strain relationship of reinforcement soils under different layers and principle of equivalent confining pressure, strength properties of reinforced expensive soils with failure material were analyzed. Mohr circles of different reinforcement layers were tangent to the same line while reinforcement materials fractured. With the increment of axial pressure, different layers were fractured slowly and Mohr circles extended outward. It showed that the strength of reinforcement soils increased with increasing the layers. And the tri-axial tests showed that strength envelopes of reinforcement soils with layers of flexible materials were approximately parallel. The increment of strength was only affected by increment of cohesion.