Based on the non-equilibrium themodynamic theory, the thermal driving forces and the fluxes in heat and mass transfer process for unsaturated soil were analyzed. The. mechanics of heat and mass transfer in unsaturated soil were discussed and the phenomenological equations to describe the transport process in unsaturated soil were established. By means of the diffusion law and the equation of state for ideal gas, the expressions of the coefficients in the phenomenological equations were deduced. The effects of temperature, water content and partial vapor pressure on the phenomenological coefficients were also discussed.