Abstract: Intermittent abnormal vibration and noise is generated in the air conditioning system of an electric vehicle, which seriously affects the driving comfort. Firstly, the fault parts are identified as compressor and cooling fan by the separate operation method. The fault is confirmed to be the beat vibration by the structural analysis of parts, the theoretical analysis of beat vibration and the analyses of time domain data and spectrum. Then, the mechanism of the beat vibration is confirmed by transmission path analysis and test. Finally, for the two key components of compressor and cooling fan, a variety of improvement measures are proposed in terms of source and transmission path, and the effectiveness is verified by the parts and vehicle tests. The results show that the beat vibration can be effectively eliminated by reducing the excitation of vibration source and improving the vibration isolation of transmission path, and the vehicle interior noise can be reduced by 8.1 dB(A), the reduction ratio is about 13.94%.