The relationship between air permeability and pressure difference between fabrics is measured. Six fabrics which have same yarn linear density, threads per 10 cm and different picks per cosity and inertia of air flow exists. The regression equations were calculated for △P=＞au + bu , with the correlation coefficient greater than 0.98. The relationship between factors a, b and cover-factors of fabrics, E, are analyzed and calculated and expressed in hyperbola equations.