Abstract: The mechanical properties of biomaterials are closely related to their structural design in nature. The flexible biological materials mostly are designed as hierarchical structure that has the unique feature of gradient, which makes the materials have good deformation capacity as well as toughness. In this paper, the concept of bioinspired flexible structural elements was put forward that based on the basic elements of engineering structural design. The bionic elements were divided into line elements, beam elements, column elements, plate and shell elements, thin film elements and composite elements according to the geometrical morphology. The design system of bioinspired flexible structure was developed from the point of view of system theory. The design criterion of flexible bionic structure was summarized. A novel bionic functionally gradient plate was design based on the gradient structure of fish scale. The normalized-dimensionless natural frequencies of functionally graded plate were computed by the finite element method, the results show that the functionally graded plate, inspired by the structure of fish scale, has the characteristics of flexibility and stiffness softening. Finally, the natural function of flexible biomimetic methods is discussed in detail, including imitation design, combinatorial design and matching design.