Abstract: By taking two typical tensile membrane structures as examples, the free vibration properties of membrane structures were investigated using the Block Lanczos method, and the effects of stiffness of strengthened cables, prestress on membrane, ratio of rise to span and mass of membrane were discussed. The results show that the prestress and the mass are the two most important factors influencing the free vibration properties, and the geometry update resulted from large deformation has also a great effect on the free vibration properties. Finally, the concept of mode analysis considering the geometry update was put forward based on the effect of nonlinear large deformation on geometric stiffness of membrane structures.