Abstract: Dual active bridge converter is widely used in energy storage, traction, DC power transmission due to its good performance in soft-switching, electric isolation and power control ability. Modulation strategy, which decides the current in primary /secondary side and the switching time of the switches, is important for dual active bridge and has great influence on efficiency. The power loss of switches can be calculated under certain modulation strategy. In this paper, an optimum efficiency orientated modulation strategy is proposed. The conduct loss and switching loss are both considered based on the different working mode of dual active converter, and the modulation with lowest total losses and best efficiency can be chosen. The PLECS simulation results show the correctness and effectiveness of proposed strategy.