Because of the advantages of excellent power, fuel economy and zero-emission characteristics, electric buses have been used widely as cities’ short-range commuter vehicles. However, the high-frequency noise becomes more prominent for the powertrain system of the electric bus due to the lack of noise masking effect for the traditional internal combustion engine. To improve the noise characteristic of electric bus powertrain, the identification of the main noise source of the powertrain is well needed.In this paper, the effects of the motor and transmission on the noise level of the electric bus powertrain have been studied using lead packaging method. The variations of acoustical power level of the powertrain according to different rotation speed and torque under the conditions of only motor covered and only transmission covered have been discussed. The operation range of the powertrain has been divided into three regions and are defined as low speed/high torque region, high speed/low torque region and normal operation region, respectively. In addition, a concept of Noise Contribution Index (NCI) has been introduced to evaluate the contribution of the motor and transmission to the overall powertrain noise level in the above mentioned three operation regions.Results showed that for the low speed/ high torque region and normal operation region, the noise level of the powertrain depends on the transmission noise level, but for the high speed/ low torque region, it changed to the motor noise level. In additions, from the results of the correlation analysis, it showed that the variations of the motor noise level were mainly attributed to the rotation speed, while the variations of the transmission noise level were mainly attributed to the torque.