In marine integrated power systems (IPS), dc/dc converters have been widely used to buffer the power of pulsed loads. However, limited by ship space and safety, its buffering capacity and volume are conflicting and need to be balanced. Existing methods usually oversimplify the switching dynamic process caused by the different switching periods between the pulsed loads and converters, leading to oversizing or underpowering issues of the converts. To overcome this hurdle, this article proposes a millisecond-time-scale-based state-space averaging mode (MTS-SSAM) to analyze the dynamic process by taking pulsed loads period instead of the traditional converter period as the averaging operator. Based on MTS-SSAM, taking the system allowable voltage and current fluctuation rate and converter volume as the objective function, the converters' parameters are optimized considering the balance between buffering capacity and volume. The proposed parameters optimization method can save 49% converter volume compared with existing methods. The simulation and experimental results are presented to verify the proposed SSAM and optimization method.