To reveal detailedly the strength and stiffness characteristics of biaxial warp-knitted fabrics，which contain multi-layered composite structures，high performance biaxial warp-knitted fabric Seaman PVDF8028 was taken as the research object，and seven tensile tests of off-axis angles with a gradient of 15° were performed. Based on the obtained stress-strain relationship, strength and deformation data of different angles, the relationship between elastic modulus and strain was deduced, and its evolution was analyzed minutely. The results show that biaxal warp-knitted fabric PVDF8028 is a typical nonlinear and anisotropic material. Stiffness characteristics of different angles present obvious differences and evolve regularly. In the whole tested strain range, the stress-strain relationship and elastic modulus-strain relationship exhibit three distinct sections, including the initial linear elastic section，strain hardening section, and stress hardening section. Additionally，there is a “W” shaped relationship between tensile strength and off-axis angles, which is different from the “U” shaped relationship of Tsai-Hill strength criterion. The results can provide some useful references for strength prediction and deformation analysis of biaxial warp-knitted fabrics, as well as the design and analysis of membrane structures.