A new definition of generalized equivalent confining pressure is proposed in term of that the function of reinforcing material in the reinforced soil is equivalent to confining pressure. Expression of the generalized equivalent confining pressure is set out by difference of confining pressures between reinforced and un-reinforced soil samples at the same strength. And limited balance equation of reinforced soil

in which 2 indexes (?

?) are used to estimate the strengthening effects of the materials

is carried out according to the fact that the Mohr-Coulomb theory is also obeyed in reinforced soil. The tests of laterite reinforced by flexible materials show that

the index ? is close to 1 in different drainage conditions

and the index ? varies with drainage conditions in which it is greater than 1 when drained entirely and smaller than 1 when not drained; and it is related to rows and properties of the reinforcing materials when concreted but un-drained

the generalized equivalent confining pressure is minus when not drained or concreted but not drained and positive when drained entirely. The index ? and the generalized equivalent confining pressure increase when more materials used.