In this paper, a high frequency wide voltage range CLLC resonant converter is designed. The high voltage side is 400V, while the low voltage side is 35-50V. By the utilization of Gallium Nitride(GaN) device and the optimization of the circuit, the resonant frequency of the converter is set as 500kHz, and the power density reaches 4.1W/cm3, and the maximum efficiency reaches 96.24%. Meanwhile, to further widen the voltage range of the converter, a hybrid modulation method which combined the phase shift modulation and frequency modulation is proposed. It helps the resonant tank realize a wider gain range. And the transfer function of the converter in two modulation methods are calculated by the simulation, and the compensators are designed. What's more, to smoothly switch between these two modulation method, an optimized switching method is proposed. What's more, a synchronous rectification method conducted by the DSP is introduced. Finally, a soft start method by increasing the starting switching frequency is adopted to reduce the overshoot in starting procedure.