Taking example of a four-cylinder inline diesel engine that used in vehicle, this paper makes an assembly engine of three-dimensional that based on virtual prototype technology. While using the flexible-body dynamics simulation, the main bearing load that effect engine’s vibration will be gained. And the key point vibration response will be gained when the support part constrained. The experimental results coincide with the simulation results shows the correction of the simulation analysis. The initial stage of the vibration can be predicted by using the method of multi-body system analysis, and this guide the designer to identify the engine vibration.