Taking into account the coupling of rotor whirl and drum vibration, the dynamic model of a disk-drum-shaft system is established for the drum-disk type rotors in turbo-machines. Based on this model, effect of the unbalanced rotor whirl on drum vibration is studied in this paper. The results show that the unbalanced rotor whirl is coupled with the drum vibration modes which carry one circumferential wavenumber. If the support stiffness of the shaft is linear, the centroid motion locus of the shaft will be a circle and the steady-state vibration cannot be maintained. However, the centroid motion locus will be complex provided that the support stiffness of the shaft is nonlinear. Under this circumstance, slight and steady-state vibration of drum will be induced by the whirl of the unbalanced rotor.