In examining potential host rocks for such purposes as the disposal of high-level radioactive wastes,it is important to understand the coupled thermo-hydro-mechanical(THM) behavior of a porous medium.A rigorous and fully unified coupled thermo-hydro-mechanical model for unsaturated porous media is required to simulate the complex coupling mechanisms involved.Based on modified Darcy’s and Fourier’s laws,equations of mechanical equilibrium,mass conservation and energy conservation are derived by introducing void ratio and volumetric liquid water content into the model.The newly derived model takes into account the effects of temperature on the dynamic viscosity of liquid water and void ratio,the influence of liquid flow on temperature gradient(thermo-osmosis),the influence on mass and heat conservation equations,and the influence of heat flow on water pressure gradient and thermal convection.The new coupled THM constitutive model is constructed by a finite element program and is used to simulate the coupled behavior of a tunnel during excavation,ventilation and concrete lining stages.Oil and gas engineering,underground disposal of nuclear waste and tunnel engineering may be benefited from the development of the new model. In examining potential host rocks for such purposes as the disposal of high-level radioactive wastes, it is important to understand the coupled thermo-hydro-mechanical (THM) behavior of a porous medium. A rigorous and fully unified coupled thermo-hydro-mechanical model for unsaturated porous media is required to simulate the complex coupling mechanisms involved. Based on modified Darcy’s and Fourier’s laws, equations of mechanical equilibrium, mass conservation and energy conservation are derived by introducing void ratio and volumetric liquid water content into the model. derived model takes into account the effects of temperature on the dynamic viscosity of liquid water and void ratio, the influence of liquid flow on temperature gradient (thermo-osmosis), the influence on mass and heat conservation equations, and the influence of heat flow on water pressure gradient and thermal convection. The new coupled THM constitutive model is constructed by a finite element program and is used to simulate the coupled behavior of a tunnel during excavation, ventilation and concrete lining stages. Oil and gas engineering, underground disposal of nuclear waste and tunnel engineering may be benefited from the development of the new model.