In order to implement the systematic analysis and prediction of differential mode conducted interference of power electronic devices, a method is proposed based on system identification to describe the characteristics of differential mode conducted interference coupling channel. This paper selects Buck converter as the research object, exerts Pseudo Random Signal (PBRS) between MOSFET drain-source as input signal and takes differential mode interference of power supply side as output signal. According to the extracted data, the system model of coupling channel is identified by the least square method. It is indicated that the experimental waveforms are consistent with the coupling channel model prediction results in terms of the time domain and frequency domain. Measuring the interference voltage between the drain-source of MOSFET as the input signal by use of the built model can predict the conducted interference of power supply side and achieve good results with the relative few measurements. This work is supported by National Key Research and Development Program of China (No. 2016YFC0600906).