Taking the propulsion shafting of 10000 DWT low-speed diesel engine as the research object, the equivalent system model is created to analyze the free vibration of the propulsion shafting based on the system matrix method, and the torsional vibration natural frequency and vibration mode are obtained. At the same time, the gas and reciprocating inertia excitation moment of the diesel engine at full speed is studied, and the frequency domain steady-state torsional vibration response characteristics of the propulsion shafting under the joint excitation of the diesel engine and the propeller are calculated to obtain the main harmonic and resonance speed points of the shafting torsional vibration, as well as the stress values of the components of the propulsion shafting. The results show that when the shafting vibrates at low frequency, the amplitude of the cylinder and intermediate shaft is large, and the shafting stress is far less than the yield strength of the material. The ship can sail safely and stably, and lay a foundation for the research of transient torsional vibration of shafting in time domain.