Abstract: Presents a torsional vibration model during the flameout of a cylinder with the system matrix method.Simple harmonic analysis was carried out for the excitation torque acting on a single cylinder both under normal combustion and when facing the flameout of a cylinder. Further,simple harmonic analysis results were obtained for the excitation torque of multi- cylinders in V- style and in line cylinder engines.Torsional vibration calculation was completed for the powertrain ofa vehicle equipped with V- 6engine under two conditions—— normal ignition and the flameout of a cylinder.The results showed that the torsional vibration characteristics changed obviously,and thatthe dynamic load increased with one cylinder facing flameout.