Abstract: Airship envelope fabrics are functional laminated weave composites that behaved rather complicated nonlinear mechanical characteristics. An accurate mechanical model is the base for structural design and numerical analysis. The biaxial tensile tests of airship envelope specimens were carried out at seven tensile stress ratios. On the basis of orthotropic composites theory, the elastic engineering constants were calculated by the method of minimization of the sum of square of the strain residuals and the linear mechanical model was presented. The response surfaces of stress-elastic constants could be generated subsequently and the complete three-order polynomials nonlinear mechanical model was finally proposed in terms of stress variable. The numerical simulation of biaxial tensile at seven ratios was proposed and the results are in good agreement with the tests situation on the distributions of stress and the deformations of the slit. The stress-strain curves of simulation were compared with the experimental ones and show good consistency. In this case, the mechanical model is accurate enough for airship structural analysis.