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 noise source identification of the electric bus powertrain was studied by the method of lead packaging. The variations of the powertrain sound pressure according to different rotation speed and torque under the conditions of all exposed, only motor exposed and only transmission exposed have been discussed. The contributions of motor and transmission noise to the powertrain under whole operation conditions were obtained. In addition, the spectral analysis has been utilized to separate the main noise components of motor and transmission noise. Results showed that the contribution of the transmission noise was greater than the motor noise for the overall noise level. The results of spectral analysis indicated that the transmission noise was low-frequency noise and was mainly caused by the engagement of constant-mesh and shifting gears, on the contrary, the motor noise was high-frequency noise and mainly caused by the cogging harmonic noise and switching frequency noise. The highest sound pressure of the overall noise was appeared at the condition with high rotation speed and low torque which was mainly attributed to the transmission noise. Finally, some suggestions for the low noise design of electric bus powertrain have been provided.