This paper analyses the characteristics of the conducted electromagnetic interference (EMI) on a GaN Step-up resonant converter for electric propulsion systems. Several influential factors on the EMI emissions are investigated in the frequency range of 150 kHz to 152 MHz. For the factors, they are the value of input voltage, the dead time, the duty cycle, and the switching frequency. In the resonant converter, the value of switching frequency can result in the converter to operate in the zero-voltage switching (ZVS) or zero current switching (ZCS) operation. In addition, the impact of CM choke parameters (i.e., inter-/intra-winding capacitances) on emission mitigation are analyzed and discussed, which provides a potential guideline for the selection or design of optimal CM choke.