This paper researches differential mode (DM) conducted electromagnetic interference (EMI) in rectifier. The DM interference source generated by power electronic switches is given. Based on experimental and theoretical analysis, the conducted EMI of a three-phase rectifier is studied systematically. The study shows that it changes with resistance loads in low frequency ranges, while in high frequency bandwidth, the effect of change of the resistance load on the DM EMI is not obvious. The validity of the models is confirmed by the measurements.