This paper proposed a hydrogen production system based on a partial power converter, which only handles part of power, thus improving system efficiency. Applying dual active bridge (DAB) converter to such partial power processing circuit, there is a large voltage variation range at input port of converter, which will cause DAB converter to lose soft switching. In order to solve the above challenges, this article proposes the concept of soft switching coefficient to quantify MOSFET soft switching range, and thereby analyzes the soft switching constraints of the DAB under dual phase shift (DPS) modulation in detail. Finally, DAB converter prototype is built and tested. The experimental results show the feasibility of the system. Compared with traditional full power connection method, the topology used in this paper reduces rated power, so that the system volume and losses have been optimized.