To analyse torsional vibration of the powertrain system for series hybrid vehicle, which consisted of dynamic vibration absorber (DVA) , V12 diesel engine, speed increaser and a generator, a lumped parameter model of torsional vibration and its vibration equation is established.Based on this model, the inherent vibration characteristic is calculated by using Matlab.And forced vibration analysis including order and resonance amplitude analysis are carried out considering no-load and full-load conditions.The results indicate that the working speed chosen is appropriate.