Abstract: [Objectives] In order to analyze the transient torsional vibration characteristics of marine diesel generator under short-circuit fault, and put forward the appropriate vibration reduction and optimization scheme. [Methods] The shafting transient torsional vibration characteristics of a 20-cylinder V-type diesel generator set under short-circuit impact are analyzed by Newmark method, and the effects of different shafting parameters on shafting transient torsional vibration characteristics under short-circuit conditions are discussed. Then, a new selection scheme of shock absorber stiffness and coupling stiffness is determined. [Results] The calculation results show that the transient torsional vibration characteristics of the shafting deteriorate significantly when the short-circuit impact occurs. After optimization (the stiffness of the torsional shock absorber is optimized to 90% of the original value, and the stiffness of the coupling is optimized to 70% of the original value), the instantaneous maximum torque of the motor shaft under the short-circuit impact condition is reduced by 13.47%, and the instantaneous maximum torque of the coupling is reduced by 10.51%. The instantaneous maximum stress of each shaft section of the crankshaft is reduced by 5.29%. [Conclusions] The proposed optimized design scheme can effectively reduce the transient torsional