To address the difficulty in achieving global optimization of system performance caused by the independent design of the transformer turns ratio and leakage inductance in a dual active bridge converter under extended-phase-shift control, a coordinated optimization method for the turns ratio and leakage inductance is proposed. First, a feasible design space for the converter is established by comprehensively considering the power transfer constraint and the inductor current stress constraint. Then, the weighted average RMS inductor current and the weighted zero-voltage-switching feasibility score are introduced as evaluation indices to determine the critical turns ratio and the feasible region of optimal parameters. Finally, a modulation strategy combining offline optimization with online look-up table implementation is adopted. Simulation results show that, under the selected optimal parameter combination, the output voltage is regulated to 28V, and zero-voltage switching is achieved for the switching devices, which validates the effectiveness of the proposed method.