In this thesis, a high output current DC-DC converter with wide input voltage range based on GaN device is implemented. Generally, the volume of converter can be reduced and power density can be improved with higher switching frequency. However, the switching losses will be increased at the higher switching frequency conditions. Therefore, the characteristic of the wide band-gap device with fast switching is applied to reduce switching losses. The topology of an interleaved flyback converter with leakage inductance energy recycled is selected in this thesis. Two series capacitors are connected with input side and the voltage of each capacitor is half of input voltage. Besides, the energy stored in leakage inductance can be recycled to these two capacitors through the clamp diodes. Moreover, the system efficiency can be improved with the interleaved control method and the synchronous rectification technique. Finally, an interleaved flyback with leakage inductance energy recycled based on GaN device is implemented. The specifications of the input voltage range and output are 18V DC to 60 V DC and 5 V/30 A, respectively. The highest efficiency is 94.2% at the light load condition.