In this article the problem of two-dimensional viscous flow between slowly expanding or contracting walls with weak permeability is presented and Homotopy Perturbation Method are employed to compute an approximation to the solution of the system of nonlinear differential equations governing the problem. Comparisons are made between the Numerical solution (NM) and the results of the He’s Homotopy Perturbation Method (HPM). The results reveal that these methods are very effective and simple and can be applied for other nonlinear problems.