Abstract: A mixed finite element for coupledthermo-hydro-mechanical (THM) analysis in unsaturated porous media isproposed. Displacements, strains, the net stresses for the solid phase;pressures, pressure gradients, Darcy velocities for pore water and pore airphases; temperature, temperature gradients, the heat flux of the three phasemixture are interpolated as independent variables. The weak form of thegoverning equations of coupled thermo-hydro-mechanical problems in porousmedia within the element is established on the basis of the Hu-Washizuthree-fieldvariational principle. The proposed mixed finite element formulation isthenderived. For geometrical non-linearity, the co-rotational formulationapproach is used. Numerical results demonstrate the capability and theperformance of the proposed element in modelling progressive failurecharacterized by strain localization.