Abstract: Dual active bridge (DAB) converters are widely used in power electronic transformers, in which magnetic components have an important impact on efficiency, power density and reliability. However, previous research on the optimization of magnetic components is less combined with the operating principle of the DAB converter, the optimization problem is complicated to solve, and the inductor is rarely optimized. Focusing on the DAB converter under single-phase-shift modulation, this article combines the operating principle of the DAB converter and the multi-physics design theory of magnetic components. Using the core shape, inductance, and transformer turns numbers as decision variables, this paper establishes both circuit-level and component-level constraints, ultimately conducting multi- objective optimization to maximize efficiency and power density. For the above optimization problem, this article mainly deduces the influence of inductance and transformer turns numbers on various constraints and optimization objectives theoretically, and summarizes the design rules of decision variables, thereby reducing the dimension of decision variables. Then, the optimization process is given and finally verified through experiments.