In order to analysis the torsional vibration of the camshaft,the dynamic experiment of valve train was conducted to calculate the dynamic torque in this paper. The torsional vibration and the critical speed can be obtained by the modal analysis,and then the relationship between the torsional vibration and working condition was analyzedto confirm the torsional vibration influence to the valve train. The results show that the torsional vibration changed with the camshaft speed,and influenced the valve timingin the out of the common working condition. The camshaft torque increased obviously by taking the torsional vibration into account. The camshaft max torque and the torsional amplitude value were 4. 5 N·m and 0. 06°in the rated condition.