In recent years, the micro-grid system with wind-solar-hydrogen-energy storage has gained more and more attention. In the hydrogen production part of this system, a DC/DC converter is needed to connect the DC bus and the electrolyzer load. Based on the characteristics of electrolyzer load, this paper proposes a combined input series output parallel (ISOP) DC/DC converter for hydrogen production based on multi-resonance theory, which can achieve high step-down ratio, low voltage high current output capability and low ripple output current. In addition, according to the actual situation, this paper analyzes the causes of the input voltage imbalance problem that may occur among converter modules by exploring the effect of the difference in resonant parameters of converter modules on the magnitude of the imbalance between modules. In order to achieve the power balance among the modules of this combined topology, the control method suitable for this hydrogen converter is designed by combining the operating characteristics of the electrolyzer. Finally, the design rationality of this hydrogen DC/DC converter and its control method is verified by simulation.