Abstract: In view of problem of small duty cycle existed in traditional interleaved Buck converter, an interleaved three-winding coupling Buck converter was designed by introducing three-winding coupling inductance into flyback converter. Voltage stress of switching tube and output diode of the converter were analyzed, then output voltage gain of the converter was achieved, and topology of the converter was optimized. The simulation and experiment results show that the optimized topology can suppress voltage fluctuation between both ends of switching tube effectively and reduce voltage stress of switching tube.