Abstract: Different from the metal and other materials, the soils have two basic propertios: pressure-sensitivity and dilatancy, and they do not obey the Hook’s law. Their stress-strain relationship is also divided into two types: the strain hardening and strain softening. For drained triaxial shear tests, a new shear curve describing mode and a new volume deformation curve describing mode are proposed respectively. Each mode contains four parameters, and the physical meaning of each parameter is clear and easy to identify. Combined with the three-parameter nonlinear elastic model by Sheng Zhu-jiang, a modified model is proposed initially. The modified model is verified by the data of a set of drained triaxial shear tests. The results show that the modified model can reflect both strain softening and dilatancy of soils reasonably. In addition, it can also describe the features of soils at small strain state, high nonlinearity of stiffness and high modulus accurately.