In view of one 4-cylinder gasoline engine with no TVD fitted having a risk of exceeding the limit of crankshaft system torsional vibration,an optimization is conducted by using a method of simulation and engine test.According to the study results a TVD of 356Hz inherent frequency is chosen to decrease the overall torsional angel below 0.5 ℃ A.In the meantime,a study is implemented to analyze the influence of the TVD of different inherent frequency to the crankshaft torsional vibration.