Abstract: Aiming at the application fields of low voltage input and high voltage output, a push-pull LLC resonant converter with high gain and high efficiency is proposed. By embedding the LLC resonant circuit on the secondary side of the push-pull converter, the zero-voltage turn-on of the MOSFET is realized | the transformer design adopts the structure of the primary side in parallel and the secondary side in series, which realizes the energy conversion of the primary side low voltage and large current, and the secondary side high voltage and small current. Based on the detailed introduction of the converter's topology and working principle, the selection of key parameters k and Q parameters and the realization conditions of soft switching are analyzed. Finally, a prototype test prototype of 12V input and 350V/500W output was built. The test results show that the converter has the advantages of high gain and high efficiency, and is suitable for low voltage input and high voltage output