The "dynamic stiffening" phenomenon in flexible multi-body system dynamics is due to the deformation coupling. The first-order approximation model has been successfully used for the rigid-flexible coupling modeling in small deformation. However, it is found necessary to consider more deformation coupling effects in lager deformation cases. In this paper, the beam bending curvature and axial strain are selected as the element parameters; Then the recursion formulations are obtained for the kinematic parameters of two nodes of an element based on theories of large deformation and finite rotation. A planar beam element used for large deformation rigid-flexible dynamics analysis is proposed, which can automatically take into account the "dynamic stiffening terms". Finally, the validity and effectiveness of the proposed algorithm are verified through some numerical examples, which involve the large deformations and rigid-flexible dynamics of beams.