The permeability of textile reinforcements is a crucial input for the simulation of the impregnation stage of a composite material fabrication process. In this paper, we present a fast and accurate simulation method for the permeability of a textile reinforcement, based on a finite difference discretisation of the Stokes equations. Results for single layer, multi-layer and sheared models are discussed. The influence of intra-yarn flow and periodic or wall boundary conditions are considered. We compare the numerically computed permeability values with experimental data.