Abstract: The modified secant modulus formula derived from the hyperbolic stress-strain relation is presented in this paper. Based on this proposed formula an analysis was made for the earth dam located in Hubei province, At the same time, similar analysis was also carried out by using the tangent modulus formula derived by Duncan and Chang. The modified modulus formula described in this paper evade the difficulties and the testing work involved in determing the initial modulus of the stress-strain curve as required by the Duncan-Chang equation. The concept of pre-consolidation pressure for soil is employed to modify the formula of initial modulus appeared in Duncan’s equation when minor principal stress is very small. Comparison of the calculations based on these two formulas revealed that the final results obtained by Duncan’s formula were influenced by initial modulus significantly while that by modified secant formula is independent of the initial modulus, and moreover, the final results obtained by modified secant formula are in agreement with that from observations.