The two-stage aviation static inverter requires the front-end DC-DC converter to ensure stable bus voltage when the voltage input is between 18 and 33 V, while also having strict requirements for reliability and efficiency. To meet the above requirements simultaneously, this article adopts an L-LLC resonant converter topology and uses a center symmetric PWM control method to regulate the output voltage. The article first analyzes the working modes of the converter when the resonant cavity is on the secondary side, and obtains the time-domain relationship of voltage and current under each mode. Based on the above analysis, the voltage gain formula of the converter was derived, and the loss relationship of each part of the converter was analyzed. For the optimization design goal of high efficiency, the design methods of excitation inductance and auxiliary inductance were proposed. Finally, an experimental prototype with an input of 18–33 V and an output of 190 V/1100 W was developed, with a peak efficiency of 96.6%, which verified the correctness of theoretical analysis and design.