Aiming at the issue of significant backflow power in dual-active-bridge converters under advanced dual-phase-shift control when input voltage, output voltage, and transformer ratio are mismatched, a backflow-power optimization control strategy is proposed. First, new dual-phase-shift ratios are redefined based on the phase relationship between the midpoint output voltages of the primary and secondary H-bridges and the internal phase-shift angles of the full bridges. The operating modes are divided into eight intervals. Then, four intervals for forward power transfer are selected for analysis, deriving mathematical expressions for transmission power, backflow power, and current stress. Subsequently, a segmented optimization approach is employed to determine the optimal phase-shift angle combinations in different intervals, yielding the expression for minimum backflow power. An advanced dual-phase-shift modulation strategy with minimum-backflow-power optimization is designed, enabling adaptive selection of the optimal operating interval and corresponding phase-shift angles. Finally, an experimental prototype of the dual-active-bridge converter is built. Results show that compared to traditional dual-phase-shift control, the proposed strategy significantly reduces current stress and backflow power while improving efficiency. At a voltage conversion ratio of 2.5, current stress is reduced by 48.3%, backflow power by 89.1%, and efficiency is improved by 9.4% in the low-power range, in the medium-power range, current stress decreases by 30.3%, backflow power by 92.5%, and efficiency improves by 10.7%. At a ratio of 1.5, current stress is reduced by 34.8%, backflow power is completely eliminated in the low-power range, and efficiency rises by 8.1% in low-power range, in medium-power range, current stress reduces by 45.3%, backflow power by 92.9%, and efficiency increases by 9.3%. The results validate the correctness and effectiveness of the proposed design.