This paper proposes a high-order resonant converter based on switched capacitor pre-buck. The converter has good voltage gain characteristics and can realize soft switching in the full load range. The stacked structure of the switch capacitor on the front stage of the converter effectively reduces the voltage stress on the device, and at the same time, the bus voltage can be pre-dropped, which is suitable for occasions with high step-down ratio. Through reasonable parameter design and frequency matching in the latter high-order resonance link, the third harmonic is superimposed in the energy transmission process. The loss of the secondary side rectifier diode is significantly reduced, and the efficiency is improved. This article introduces the working principle of the converter and conducts experimental verification. A 100 W prototype with 400 V input and 12 V output was built in the laboratory to verify the correctness of the theoretical analysis.