Medium voltage solid-state transformers is one of the key equipments for the medium voltage DC power grid in ships to achieve voltage conversion and electrical isolation. The traditional modular structure of high-voltage side series and low-voltage side parallel (Input-Series Output-Parallel, ISOP) requires the use of a large number of isolation transformers, which have low power density and complex control. This paper designs a megawatt-level intermediate voltage DC solid-state transformer solution that combines module ISOP and power devices in series for marine 10 kV medium voltage power distribution system. The main circuit adopts the ISOP topology structure of two half-bridge resonant LLC converter modules; the fundamental wave equivalent method is used to design the LLC resonance parameters, the LLC DC capacitance capacity is designed according to the fluctuation requirements of the capacitance voltage, the LLC power device is selected based on the voltage and current stress, and the output voltage and equalization strategy between the modules is designed based on the frequency response method. It is proven that the dynamic and steady-state simulation results are consistent with expectations and the solution is feasible.