Abstract: In this paper, the modeling theory of rigid-flexible coupling dynamics of aflexible beam with three-dimensional large overall motion is studied. Basedon the precise strain-displacement relation, the rigid-flexible coupling dynamicequations are derived using the velocity variational principle, in which thevirtual power of the torsion force and the inertial torque of the beamelement are included and the geometric nonlinearity is taken into account.Finite element method is employed for discretization. Simulation of aspatial beam system is used to show the influence of torsion and crosssection rotary inertia on the dynamic performance of the system.Conservation of energy in case of free motion is shown to verify the proposed nonlinear model. It is shown that the torsiondeformation influences not only the axial angular velocity of the hub,but also the lateral angular velocity of the hub and the bendingdeformation of the beam.