To address the issue of rational energy storage configuration in off-grid hydrogen production systems, this paper proposes an optimized configuration method for energy storage in such systems. Firstly, the supporting role of grid-forming energy storage in the voltage and frequency of off-grid systems is analyzed, clarifying the grid-connection approach using grid-forming energy storage as the power source for off-grid system. Secondly, based on the configuration of renewable energy off-grid hydrogen production systems, a control strategy for energy storage to support black start of off-grid systems is formulated. Thirdly, an optimized energy storage configuration model considering the unit cost of hydrogen production and the system’s electricity curtailment rate is established, and the particle swarm optimization algorithm is employed to solve the model. Finally, the Datang Duolun Wind and Solar Hydrogen Production Project is selected as the research object. Through economic evaluation and stability analysis of the off-grid hydrogen production system, the effectiveness of the optimized energy storage configuration method for off-grid hydrogen production systems is verified.