Abstract: This paper proposes a high-voltage high-power LLC resonant converter design method and dead time design optimization method for the photovoltaic DC voltage boosting conversion system. The application scenario of the high power LLC converter, the system architecture and module topology of the photovoltaic DC voltage boosting converter are introduced. Then the time domain model of the LLC converter is established based on the modal analysis method, and its solution method is studied. The differences between high-power and low-power LLC converter design are analyzed, and the low-power converter design method cannot be followed. Therefore, an accurate and simple design method for high-power LLC converters is proposed based on the original parameters and time domain model solving method, with high efficiency as the goal. In addition, a dead time design optimization method is proposed based on modal analysis. The theoretical study and the proposed method are validated on a prototype 80kW/5kV photovoltaic DC voltage boosting converter.