The isolated DC/DC converter connects the low-voltage direct current (LVDC) distribution network and the user-side DC load serving as an important equipment in LVDC distribution network. In this paper,LLC resonant converter with zero voltage switching on primary side and zero current switching on secondary side is adopted. The operation principles of LLC resonant converter are analyzed and the resonant parameters are presented. The gallium nitride device with lower on state resistance and effective output capacitance is used as the primary side switches to increase switching frequency and efficiency,thus decreasing magnetic component volume. Then,the driver of GaN devices,synchronous rectification and magnetic components are optimized and designed. Finally,a 375 V/48 V/500 W LLC resonant converter prototype is applied to verify the correctness of the design. The peak efficiency of the prototype is 97.6%,which is about 1% higher than that of the converter using traditional Si devices.