The Dual Active Bridge (DAB) DC-DC converter is one of the most popular circuits for bi-directional applications because of simple structure. However, DAB DC-DC converter has few problems such as the surge voltage and hard switching in specific conditions. These problems are caused by the relationship between the output power and phase difference, which causes device breakdown and deterioration of power efficiency. For the design of Input-Series and Output-Parallel (ISOP) converter system with DAB DC-DC converter, the problem is also occurred and more severe because of its high voltage. In this paper, the design technique of ISOP with DAB for suppressing the surge voltage and realizing the high power efficiency in wide load range is proposed. As the result, this method reduces the switching surge, and the power efficiency is increased by 22.5% at light load.