Based on the relationships between the Hvorslev envelope,the current yield sur-face and the reference yield surface,a new constitutive model for overconsolidated clays is proposed. It adopts the unified hardening parameter,to which the potential failure stress ratio and the characteristic state stress ratio are introduced. The model can describe many characteristics of overconsolidated clays,including stress-strain relationships,strain hardening and softening,stress dilatancy,and stress path dependency. Compared with the Cam-clay model,the model only re-quires one additional soil parameter which is the slope of the Hvorslev envelope. Comparisons with data from triaxial drained compression tests for Fujinomori clay show that the proposed model can rationally describe overconsolidated properties. In addition,the model is also used to predict the stress-strain relationship in the isotropic consolidation condition and the stress paths in the undrained triaxial compression tests. Based on the relationships between the Hvorslev envelope, the current yield sur-face and the reference yield surface, a new constitutive model for overconsolidated clays is proposed. It adopts the unified quenching envelope, where the potential failure stress ratio and the characteristic state stress ratio with introduced. The model can describe many characteristics of overconsolidated clays, including stress-strain relationships, strain hardening and softening, stress dilatancy, and stress path dependency. Compared with the Cam-clay model, the model only re-quires one additional soil parameter which is the slope of the Hvorslev envelope. Comparisons with data from triaxial drained compression tests for Fujinomori clay show that the proposed model can rationally describe overconsolidated properties. In addition, the model is also used to predict the stress-strain relationship in the isotropic consolidation condition and the stress paths in the undrained triaxial compression tests.