Abstract: In flyback converter, transformer windings are interleaved to reduce leakage inductance and winding losses,but the inter-winding capacitances are the main coupling path of common mode（CM） conducted noise, which can cause severely electromagnetic interference（EMI） problems. To mitigate the CM noise and improve flyback converter power density simultaneously, a group of balance windings were introduced. The displacement current between balance windings and the adjacent secondary winding have the same amplitude and opposite direction, so the CM current that injects across transformer can be cancelled each other. The CM conduction noise model of flyback converter was established,and the design method of balance windings was given. A flyback converter prototype was built, and the CM noise of the flyback converter was measured and compared using three different transformers including without shielding layer, with traditional shielding layers and adding balance windings. The experimental results reveal that the balance windings are superior to without shielding layer and with traditional shielding layers, also verified the effectiveness of the balance windings on cancellation the CM noise.