Abstract: The constitutive model for geomaterials is the important theoretical basis of geotechnical engineering. An advanced constitutive model can qualitatively reveal deformation and strength mechanisms of geomaterials, and also quantitatively calculate the deformation and strength. The author has been devoted to the constitutive model for geomaterials for more than twenty years and obtained the following theoretical achievements: (1) The unified hardening (UH) model is established. Using the same soil parameters with the Cam-clay model, the UH model can describe shear contraction and dilatation, strain hardening and softening as well as stress-path-dependency of saturated overconsolidated clay. (2) The UH model is extended to consider influences of some external factors (temperature, time and suction), complicated characteristics (anisotropy, structural and small-strain properties) and complicated loading paths (cyclic loading, and various drainage conditions, namely asymptotic states). (3) The generalized nonlinear strength criterion and the transformed stress method satisfying the thermodynamic laws are proposed in order to generalize reasonably the constitutive model to the three-dimensional stress space. The UH model has been embedded into the commercial numerical analysis software and applied to the geotechnical engineering analysis. This research framework involves constitutive modeling, strength criterion, generalizing method and numerical analysis, forming a unique constitutive theoretical and applicable system.