The thermo-visco-elasto-plastic constitutive model describe the stress-strain relationship of soil under the combined effect of temperature and time. In the construction of some new-type geotechnical engineering, such as nuclear waste disposal as well as geothermal extraction and storage, it is necessary to consider the influences of both temperature and time. Therefore, it is theoretically and practically meaningful to establish a thermo-visco-elastoplastic constitutive model. Firstly, an isotropic stress-strain-time- temperature relation is established by considering the temperature effect on clay volume and strength parameter into the isotropic stress-strain-time relation. Afterwards, hardening rules are deduced from the isotropic stress-strain-time-temperature relation. Through combining the hardening rules with the yield functions of the unified hardening constitutive model, a thermo-visco- elastoplastic constitutive model for overconsolidated clay is proposed. Finally, the proposed model is used to predict laboratory tests. The predicted results show that the proposed model can describe the combined effect of temperature and time on the clay volume, the isotropic compression curve and the preconsolidation pressure.