Abstract: The equations with coupled boundary condition on the interface,which govern the process of pressured water infiltration and pore gas expelling in unsaturated soils,are established in this paper based on the equilibrium analysis for pore water and pore gas separately. It presents a new method to solve the problems of water infiltration. Examples of applying the method to 2-D numerical simulation of the process of pressured water infiltration in dry sand and fly ash are given. The results of the simulation show the influence of pose gas expelling on the water infiltration process. Comparisons of numerical simulation by the method and theoretical solution for one-dimensional problems are illustrated. It shows that the proposed method is accurate.