The free energy and dissipation function for over consolidated clays are established

which are based on the generalized thermodynamic method and combined with the thermodynamic functions form of the modified Cam model. The energy generated by the plastic shear deformation is considered a part of free energy in the free energy function

and this partial free energy is related to the degree of over consolidation. When the degree of over consolidation decreases

the free energy generated by the plastic shear deformation also decreases. The dissipation function is independent of the current stress state

so the associated flow rule is still employed in this paper. Based on the free energy function and the dissipation function

all of the yield function

the flow law

the hardening law and the elastic law can be obtained with strict mathematical derivation from the two scalar functions. The final elastic-plastic incremental relation can then be obtained. Finally

the rationality of the model is verified by comparing the calculation and experimental results in stress and strain

volumetric strain of four different over consolidation clays.