In the operation of parallel hybrid electric powertrain equipped with reciprocating piston engines, torsional vibrations are present. Additionally, there is a coupled constraint effect between system torsional vibration and energy consumption, making it challenging to achieve an optimal balance between vibration suppression and energy management. To address this issue, this paper establishes a torsional vibration model for parallel hybrid power systems, analyzes the coupled constraint effect between system torsional vibration and energy consumption. Building on this, a hierarchical control method is proposed that considers the optimal combination of system energy management and vibration suppression effects. Simulation results indicate that the proposed method can effectively reduce the system’s 2nd, 4th, 6th, and 8th harmonic amplitudes while ensuring the economic efficiency of energy consumption, thus guaranteeing the stable operation of the parallel hybrid electric powertrain.