Abstract: As a new way of distributed storage system, V2G can effectively realize load stabilization and regulation of power grid, and is easy to produce huge economic benefits. Dual active bridge converter is an important part for V2G, which has good electrical isolation and power conversion ability. However, V2G needs bidirectional power ability, wide output voltage range and wide power range, which complex the design of dual active bridge converter. In this paper, a design method of dual active bridge based on the optimum efficiency is proposed, which can consider all the parameters, such as frequency, device, power, magnetic component, control method, output voltage range and input-output voltage relationship, and obtain the dual active bridge converter with optimal efficiency.