Electromagnetic interference ( EMI) inside the microwave source case can couple outside along the power lines to affect other power electronic equipment when it is working. There exists many literatures for research on conducted EMI of the three-phase input power lines, in which the separated common-mode ( CM) current and differential-mode ( DM) current between three-phase lines are only considered, but the analysis of conducted EMI on neutral line is absent. In this paper,a current sensor, which is cali-brated in a vector network analyzer, is used to measure the conducted EMI of 3 kW magnetron microwave source power lines, then the interference current on phase line and neutral line at 150 kHz~30 MHz is ob-tained, and the CM and DM current is separated. EMI mode on the neutral line is analyzed by comparing the DM current spectrum with the interference spectrum on the neutral line. The tested data shows that DM interference magnitude is above 10 dB larger than CM interference at 150 kHz~8 MHz, and the phenome-non that interference on neutral line and DM interference show a good concordance in terms of peak value indicates DM interference is in dominant on neutral line. Knowing about these interference distribution is helpful for proposing efficient interference suppression method.%微波源工作时内部的电磁干扰可以通过电源输入线耦合出来，干扰其他电力电子设备。研究三相输入电源线的传导干扰文献很多，但分离的共模( CM)和差模( DM)电流局限于相线之间，缺少对中线上干扰的分析。使用电流探头测试3 kW磁控管微波源输入线的传导干扰，利用矢量网络分析仪校准电流探头，从而获得150 kHz~30 MHz频带内相线和中线的传导干扰电流，并分离出CM电流与DM电流。通过对比DM电流和中线上干扰的频谱，分析了中线上传导干扰成分。测试数据表明，在150 kHz~8 MHz频带内差模干扰电流比共模干扰电流大10 dB以上；中线上的干扰与DM干扰幅值一致，表明中线上的干扰主要是差模成分。该干扰分布规律有助于提出有效的干扰抑制手段。
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