Abstract: In order to study the biaxial shear mechanical performance of the polyester fabric-polyvinyl chloride-polyvinylidene fluoride (P-PVC-PVDF) membrane, the calculation formula for engineering shear strain, the modified formula for shear stress, and the method for stress loading were given. The biaxial shear test of P-PVC-PVDF membrane was then carried out using a self-developed biaxial tensile tester. The shear stress-strain curves, shear modulus and hysteresis loop area were obtained. The analysis results show that the mechanical parameters are different when the direction of shear stress is changed. However, all the mechanical parameters turn stable after the first loading cycle. The range of stable shear modulus is 11-13 kN/m when the up and lower limit of shear stress is set to be ±2 kN/m. The change of the angle between the principle axial and the direction of loading has little influence on the calculation result. These results can be useful for the analysis and design of membrane structures.