Aimed at the problem of low efficiency of a dual active bridge (DAB) converter in the wide voltage range of single phase shift modulation strategy, a one-sided asymmetric duty modulation strategy is proposed in this paper, which significantly improves the efficiency of DAB converter, especially in the case of light load. First, the principle of one-sided asymmetric duty modulation scheme is described, and two operation modes are obtained according to the relationship of control degrees of freedom. Second, based on the time-domain analysis, the steady-state characteristics in the two operation modes are derived, including inductance current and transmission power. Third, in order to find the optimal combination of control degrees of freedom, the peak-to-peak value of inductance current is selected as the optimization objective, and the optimal one-sided asymmetric duty modulation strategy is obtained by applying the KKT condition. Finally, an experimental platform for DAB converter based on SiC device was built, and experimental results verified the effectiveness of the proposed one-sided asymmetric duty modulation strategy.