In this paper，the dynamic modeling and vibration characteristics of an internal flexible beam system on a steadily rotating ring are studied. The floating frame reference method is adopted，in which the axial shortening of flexible beams due to bending deformation is considered. The displacement field of the flexible beam is interpolated by finite element method，and then the expressions of the kinetic energy，strain energy and work done by gravity can be derived. Using the second kind Lagrange’s equations，the dynamic model of the internal flexible beam system on a steadily rotating ring is established. Based on this model，the critical instability speed of the system is analyzed. The simulation results are consistent with the data in the existing literature and the numerical results obtained from commercial software ANSYS，which can validate this model. Several findings observed clearly in the numerical results are as follows：There is resonance speed of the system which is smaller than the critical instability speed. In the case of the resonance speed，the frequency of gravity periodic change is close to the natural frequency of the system，and then the vibration amplitude of the beam increases with time. The larger ratio of diameter to length will be result in the smaller resonance speed.When the ratio of diameter to length is 1，the resonance speed region is approximately from 2.20 to 2.36. If the speed is close to the resonance speed region，the vibration amplitude of the flexible beam will become larger or smaller from time to time，resulting in beat vibration phenomenon.