Abstract: A non linear model for unsaturated soils is presented. The model consists of two aspects, i.e., the deformation of soil skeleton and the water volume change of unsaturated soil. Total of 13 parameters are involved in this model, 11 of which are associated with soil structure, and 2 are associated with the water phase. All the parameters have either physical meanings or geometry meanings, and can be determined using laboratory tests. Only two types of triaxial tests are required to determine the 13 parameters, i.e., 1) the triaxial shear test with controlled suction and, 2) the triaxial shrinkage test with controlled net mean stress. The model is used to predict the suction changes in undrained triaxial tests, good agreement are obtained.