Inflatable fabric membrane has been typically used in aeronautics and astronautics, large-scale construction and other fields because of its advantages: light weight, low transportation costs, and ease of deployment and storage. However, a natural challenge is the accurate characterization of the mechanical properties of the materials such as the airbag, subjected to the anisotropy of the membrane, the interaction between the fabric and the inflation pressure. In this paper, to estimate the effective elastic constant, the biaxial tensile tests of fabric film were performed by considering the effect of inflation pressure, this and specimen size on the elastic constants was obtained. Based on the similitude theory, the reduction ratio of inflatable fabric is deduced, and the irreducible factor is analysed. The validity of theoretical derivation is verified by numerical simulation and experiment of woven airbeams loaded in four-point bending. The error of scaled model is evaluated, which provides an effective technique for large-scale inflatable structure test. Abundant research results have been achieved in the test method of fabric membrane.