Abstract: A unit cell of the non-crimped fabrics' geometrical structure was established, and the meso-level resin flow behavior within it was simulated by coupling the inter-tow and intra-tow flows. According to the Darcy's law, the equivalent in-plane permeability was calculated. And then this method was verified. Based on the above work, the relationship between the in-plane permeability of the unit cell and the meso-level structural parameters, such as the distance between fiber bundles, the fiber bundle's height and permeability, was investigated. The results show that the in-plane permeability of the unit cell increases with the increase of the distance between fiber bundles, and a positive linear relationship exists between the logarithms of their reciprocals; the height of fiber bundles has the similar effect on the permeability as the distance between fiber bundles does; the in-plane permeability of the unit cell increases linearly with the increase of the permeability of fiber bundles.