To achieve high performance monitoring of the electric transmission powerpack for a diesel multiple unit (DMU), the dynamic responses of the rotor system inside the powerpack with dynamic spatial misalignment (DSM) and base motions from car body are investigated through structural modeling and numerical analysis. A three-dimensional coupled model, including public framework, diesel engine, electric generator and rotor system, is developed. Vibrations under deterministic and random base motions are numerically calculated using the Newmark Method. The simulation results show that vibration responses of the coupled model are evidently different from those of rotors with a fixed base. DSM is more nonlinearly sensitive to the deterministic base motion than rotor vibrations, and the converse is true when the base pitch motion is random in frequency. Additionally, results show that DSM may vary significantly in different axial positions, with large base motions in some extreme situations. These findings lay the primary foundations for implementing vibration-based condition monitoring of DMU diesel-generator systems.