A passenger vehicle has various and complicated transmission paths of sound and vibration. In order to identify the mechanism of transfer path, estimation of excitation force and exact modeling of transfer path are required. In this paper vector synthesis technique is employed to identify the characteristics of road noise and its transmission to vehicle compartment through noise and vibration analysis. Vibration reduction efficiency of each transfer path is evaluated by comparing individual vector components obtained virtual simulation. The degree of effect is used to estimate the contribution of vibration input components to total output. And in this paper presents a new technique based on simulation studies using vector synthesis diagram and design of experiments, by which the effects of magnitude and phase change of input paths can be predicted.