LLC converters offer outstanding advantages when used i n data center power supply applications.To solve the problems of slow start-up of LLC resonant converters during traditional down-frequency soft starting and high MCU calculation and storage pressure in the process of optimal trajectory control soft starting，an arc resonant trajectory soft starting strategy based on trajectory control is proposed.The two charging stages of an LLC converter under the strategy are analyzed，and an adjustment stage，an entry stage，and an exit stage are designed based on the charging stages，which effectively suppresses the transient current overshoot phenomenon in the soft starting process.A PLECS simulation model and a prototype with 30 V output are developed.The simulation and experimental results show that the converter can complete the charging of a 400 μF output filter capacitor within 350 cycles，that is，3.5 ms，which verifies the correctness and effectiveness of the proposed soft starting strategy with low computing pressure.