As the switching frequency of power converters increase, electromagnetic interference (EMI) has become an inescapable issue in power electronics. Nowadays, the passive EMI filters (PEFs) are commonly used to solve electromagnetic interference problems. But in high-power systems, their large size makes them unable to meet system requirements. Nowadays, the active filters are gaining more attention for their compact size and superior performance. However, in practical applications, the AEFs often fall short in effectively suppressing high-frequency noise. Moreover, due to the poor high-frequency noise filtering effect, AEFs often can’t operate on its own and requires PEFs for supplementation. Targeting the abovementioned issues, this paper presents a hybrid EMI filter (HEF) to suppress the common-mode noise of DC-DC converters. Simulations of the buck converter verify the feasibility of the HEF, and show that the presented EMI filter effectively restrains CM EMI. The attenuation of CM EMI can reach approximately 35dB in the high-frequency range of 10 kHz to 30 MHz.