Studying membrane structure is complex due to its highly deformable property. For flapping wings made of membrane materials, this problem becomes even more challenging due to the interaction of the surrounding air and the structure. This study presents analysis results related to the deformation of biplane membrane flapping wings while operating at different conditions. The simulation program was developed in the environment of the MSC Adams software based on a mass-spring system model and a quasi-steady aerodynamic method. The results have shown that the flapping frequency may have a strong effect on the structure deformation. As the flapping frequency increases, the deformation becomes more significant; and the phase tends to be delayed. The paper also indicates that for the biplane flapping-wing air vehicle considered here, from 30 Hz, the wing deflection tends to reach its maximum amplitude, which cannot be larger as the flapping frequency increases.