This brief presented a new soft-switching auxiliary circuit for the three-level buck converter with synchronous rectification (TLBC-SR). The new zero voltage switching (ZVS) auxiliary circuit only employs one inductor and one capacitor, and has the features as full soft-switching conditions, high efficiency, low output current ripples, and simple modulation control method. The detailed operation principle and soft-switching design method are also given. Finally, an experimental prototype is built to verify the proposed ZVS TLBC-SR. The experimental results show that all switches operate under zero voltage switching (ZVS) conditions, and the peak efficiency of the prototype is up to 96.85%@100kHz.