An investigation into the dynamic modeling of rigid-flexible manipulator systems based on spectral approximation methods was presented. The nonlinear dynamic equation of the rigid-flexible manipulator was established on the theory of Lagrange equation and the model was approximated with the spectral approximation method. Furthermore, an experimental platform system was set up to validate the effectiveness of the model. Simulation results of the response of the rigid-flexible manipulators were presented. Moreover, experimental validations were carried out to assess the effectiveness of the modeling approach by comparing with the simulation results. The results verified that the method is effective and feasible.