In recent years, with the rise of China’s low-altitude economy, the eVTOL industry has been developing vigorously. To address the drawbacks of limited range and insufficient endurance in the all-electric power system of eVTOL aircraft, a hydrogen-electric hybrid power system can be adopted to provide higher energy density and conversion efficiency for the aircraft. The configuration of such a hydrogen-electric hybrid system mainly includes a hydrogen fuel cell, DC/DC converter, lithium battery, and electric drive components. A fundamental design criterion for all system components is lightweight. This paper focuses on the lightweight design of DC/DC converters, addressing aspects such as structural thermal dissipation and power drive control to achieve technical specifications of 30 kW power and 6 kg weight. The study aims to provide a lightweight power conversion solution for hydrogen-electric hybrid eVTOL aircraft.