Interconnected drive shaft (IDS for short) is an important component of drive system in tiltrotor, and dynamic stability must be evaluated during the design. According to the elastic deformation of aircraft structure, the structural dynamic equivalent modeling of typical IDS is conducted in this paper. The critical speed and dynamic response are analyzed by using rotor dynamics theory. Results indicate that under the influence of gyroscopic effect, the structural modal of IDS is changed from real mode into complex mode and bifurcate to forward whirl and backward whirl. And there are multiple critical speeds in the shaft according to the Campbell diagram. Considering the excitation by unbalanced mass, the amplitude-frequency plot shows that there are multiple frequencies components in the response of IDS that be consistent with the critical speeds, which provides an implementation method for the experimental verification of critical speeds. The amplitude-phase plot indicates that the phase relationship on both sides of IDS is related to the spatial distribution of unbalanced mass. Meanwhile, transient response analysis is used to obtain the response history during the operation for IDS, results indicate that the additional increments of displacement and stress are generated by the unbalanced mass, and the incremental responses caused by the asymmetric distribution of unbalanced mass are slightly stronger.