Abstract: In order to realize the high efficiency and high power density of the solar aircraft energy system,a four-switch Buck-Boost（FSBB）converter based on Gallium Nitride（GaN）devices is used. Firstly,a variable phase-shift angle control strategy is proposed.This control strategy can keep the inductor current ripple at the minimum value under the current operating conditions by changing the phase-shift angle according to the input voltage ranges,and at the same time ensure that the inductor current is circulating at the minimum value and take into account the soft switching technology,and further improve the working efficiency of the converter. Then,is modeled based on the converter under the proposed control strategy and its stability is analyzed. The loop design of the converter compensation network is completed by tuning the control parameters. Finally,an experimental prototype of a GaN-based FSBB converter with an input of 30-60 V and an output of 45 V/200 W was built to verify the effectiveness of the variable phase-shift angle control strategy.