As a kind of flexible fabric reinforced composites, the woven membrane materials suffer from the bi-axial tensile loads in the application of the lightweight structures. Therefore, the experiments under bi-axial tensile loads are essential for the acquaintance of the mechanical characters of the membrane materials. This paper has summarized thoroughly the details of the bi-axial tensile tests, especially the in-plane cruciform tests. The aspects include the shape and configuration of the cruciform sample, the practice of the applied stresses and the testing of the strains in the two axial directions. It could be expected to be the reference for the establishment of the testing standard of the bi-axial tensile experiment for the membrane materials.