Abstract: The effect of the fiber microstructure on the fluid flow behavior was investigated. Simulations on the fiber models which have different fiber volume fractions and nearest inter-fiber spacing were performed to calculate the fiber permeability. The results reveal that the permeability is less sensitive to the nearest inter-fiber distance when the volume fraction is low. At the high volume fraction, the permeability declines with the decrease of the nearest inter-fiber spacing. The relation of permeability standard deviation, nearest inter-fiber spacing and volume fraction was studied. The standard deviation of permeability for different fiber microstructures depends only on the nearest inter-fiber spacing when the volume fraction is low, but it is determined by both the nearest inter-fiber spacing and the volume fraction at the high fiber volume fraction.