Abstract: The effect of distributed parameters on conducted EMI was investigated for the motor drive system of an electric vehicle under load conditions. A conducted EMI testing platform was constructed for the system. By testing the conducted EMI in the system under both load and idle conditions, the propagation paths of both high-and-low frequency differential-mode noise and common-mode interference were analyzed and the equivalent circuits were established. In frequency domain, the mechanism of the conducted EMI was studied and the effect of distributed parameters on them was discussed. Tests show that high-frequency conducted EMI can be reduced by properly enlarging the distributed capacitances both between ground and power devices in the motor controller and between ground and dc-bus.