Abstract: It is observed that the necks of birds generally have the characteristics of rigid-flexible coupling and variable stiffness, which can cause large head deformation with the body movement when the bird moves as walking or flighting. In the fields such as robotics and aerospace, structures with the characteristics of large deformation, variable stiffness and rigid-flexible coupling are generally required to achieve relevant functions. Inspired by the structure of the bird neck, this paper proposes a kind of rigid-flexible coupling structure imitating the chicken neck which clarifies its bionic mechanism, and establishes the mechanical model for flexible large deformations. Firstly, it discovers that bionic structure must have the characteristics of high-degree of freedom and rigid-flexible coupling based on the biological anatomical structure of the chicken neck. A bionic single standard unit is constructed according to the characteristics of the chicken neck skeleton and a model of spring connection between nodes is constructed according to the connection mode of muscles, thus a bionic rigid-flexible coupling structure is established by combining these two elements. Then, this paper describes the distribution and function of the elastic elements between nodes by defining the connectivity matrix, with which the force balance equation of any standard rigid section under any movement is obtained. Finally, several representative working conditions are selected for simulation, which verifies the accuracy of the established theoretical modeling method by the comparation with finite element analysis, and the nonlinear variable stiffness characteristics of the structure are displayed; The relations between deformations under four typical plane bending conditions and corresponding muscles force generation are obtained. The analysis on the bionic rigid-flexible coupling structure clearly shows the characteristics of bionic mechanism of chicken neck, which gives the theoretical calculation model for large deformations, representing the nonlinear stiffness characteristics. It also explains the deformation mechanism of the chicken neck.