The dynamic modeling theory of a flexible beam which is rotating in a plane is further studied, and the highorder coupling dynamic model is investigated here. Both the transversal deformation and the longitudinal deformation of the flexible beam are considered. And the non-linear coupling deformation term, also known as the longitudinal shortening term caused by transversal deformation, is considered here. The high-order terms related to the non-linear coupling term are retained, which are ignored in the first-order approximation coupling modeling. Thus, we can get the rigid-flexible coupling dynamic equations of the system. The high-order coupling model can not only be used in small deformation case, but also in large deformation case. Then simulations, compared to the absolute nodal coordinate formulation and the first-order coupling model, are given to prove the validity of the high-order coupling model. And the results show that the high-order coupling model can make up for the deficiency of the first-order approximation coupling model in the large deformation situation.