In this paper, Electromagnetic interference (EMI) Common Mode (CM) noise is analyzed and method for noise suppression has been briefly investigated. An improved systematic design of EMI filter is proposed based on the insertion loss parameter, which takes full account of the high-frequency (HF) characteristics. In order to improve the performance of EMI filter, resonance point cancellation is introduced to improve the HF characteristics of CM inductor which is an important portion of the EMI filter. In addition, suitable winding structure and high-performance magnetic materials are also helpful for the improvement of CM inductor. Then, the layout of the EMI capacitor based on the impedance mismatch principle and its parasitic inductance effects are also discussed. Ground leakage current, as a part of the CM noise, is also suppressed by corresponding measure. As a proof-of-concept verification, the systematic design and optimization technique are validated by using a 2 kW boost PFC prototype.