In recent years, with the significant increase of the power and voltage level of earth satellites and spacecraft, more and more high-power electronic devices are gradually being used in space. However, due to the extremely complex space electromagnetic environment near the earth, very fast space transient electromagnetic radiation will have a serious impact on the use of these new electronic devices on satellites, and the power supply ports of these electronic devices are the main coupling path of electromagnetic interference intrusion. Therefore, this paper studies the electromagnetic interference coupling characteristics of space electromagnetic radiation on the power port of satellite electronic devices, and proposes a new electromagnetic interference suppression measure based on a novel LLC converter. The research results show that the high-frequency component of space electromagnetic interference at the power port will seriously affect the stability of the electronic devices' power supply, and transmit the electromagnetic interference to the output port by using the traditional DC/DC converter. The novel LLC converter proposed in this paper can effectively eliminate the coupling degree between the primary and secondary windings of the isolation transformer in the traditional DC/DC converter, and can effectively suppress the electromagnetic interference at the power port. The suppression degree of electromagnetic interference on the power port of electronic devices can reach 56 dB.