The flapping wing of large bionic ornithopters （LBOs） has obvious flexible deformation during the flapping motion， which is difficult for aerodynamic analysis. The deformation is not only affected by the flapping motion， but also related to the body motion of LBOs. This paper establishes a three-dimensional aeroelastic model of the wings of LBOs by coupling the finite element method and the finite state aerodynamic method， and combines the multi-body dynamics model established by the Kane equation method to build the flight dynamics model of LBOs. This model considers the influence of the flexible wing deformation and the body motion during the flapping process of LBOs， and can calculate the position and attitude of LBOs during forward flight. The flight states of LBOs during forward flight are computed by this model and compared with actual flight experiment data. The results show that the model can simulate the flight state of LBOs well， verifying the model’s accuracy.