The application of wide bandgap semiconductor devices makes the motor drive system of electric vehicles(EVs) more compact and lightweight, but it also causes more serious electromagnetic interference(EMI), which makes the reliability of the drive system face severe challenges. To solve this problem, a 24 V/2 A EMI DC filter is taken as an example, and through the analysis of noise source, filter principle and impedance influence, the filter parameters are designed according to the index of insertion loss. At the same time, considering the starting impact at the starting time of the whole vehicle, a soft starting circuit is added to further improve the reliability of the EV drive system. Experimental results verified the EMI suppression effect and the soft starting function of the filter, proving the feasibility and effectiveness of the filter design.