Abstract: This paper presents a coupled thermo hygro mechanical model including mass transfer process for unsaturated porous media. The numerical simulation is performed for an engineering clay barrier by using the constitutive model presented in reference1.Numerical results demonstrate the effects of environmental conditions, the heat generation in the landfill and the heat transfer process on the hygro mechanical behaviour of the clay barrier. In addition, the plastic strains leading to the failure of the clay barrier may occur. The resulting contaminant concentration distributions highlight the effects of temperature and water flux input on the contaminant transport with underground water tending to penetrate the clay barrier toward the surrounding natural clay. The numerical model and the finite element solution procedure developed can be utilized to assess the long term efficiency and referenced in the design of engineering clay barrier system.